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Quick question. Do you remember anything about setting float levels in a Nikki with Grose jets? I finally found a pair (Mike Haag) and installed them. The floats are set dead on 16mm. Fuel level in bowls wants to hang around 1/2 way up sight glass, but with pump running and engine not, the level slowly creeps up until fuel overflows. Maybe that is just a characteristic/problem with some of the Grose jets? These appear to be from the original manufacturer (D&G or something like that). I may end up going back to the stock style if I can't get this sorted.
Cheers,
Carl
Ewwwwwww setting Niki float levels. Bad memories of trial and error and hands that smelled like gas while drinking beers.
The floats on the Niki I raced with would change over the course of a weekend but not to the extent that you describe. I always attributed this to race car vibrations and the fact that fuel pressure was hard to keep constant. I typically needed to reset fuel pressure and the float levels Saturday evening during a race weekend. Optimum was 2.5PSI with with the primary floats at the half way mark and the secondaries a little below the half way mark.
Here is what I had when my car was in ITA/7
Fuel Pressure
I used an inline fluid filled 0-12PSI pressure gauge that I compared to a calibrated high quality pressure gauge we had in the shop to get true pressure values.
I used a sharpie to mark the glass on the gauge to know what 2.5PSI really was on the gauge
The regulator I used was a Holley low pressure regulator (Model 12-804)
One of the output sides was the feed side to the Carburetor using -6 AN hose
The other output side was the fuel sampling port using a short length -4 AN hose terminated with a small spigot valve
When setting fuel pressure I turned on both pumps and opened the fuel sampling spigot value and ran the fuel into a gas can to simulate that the car was running
Setting Float Level
After resetting fuel pressure I would check float levels with the engine running using an inspection mirror
If they were off I would begin the process of resetting them
I would test changes with the engine running.
Fuel System
2 Carter P4594 fuel pumps
-6 AN line from the fuel cell to the Regulator
-4 AN return line from the Carburetor back to the fuel cell
Agreed on "ewwwww". Wow! That sounds like a lot of work. I have not had to deal with that at the track, possibly because I don't have a full-time pressure gauge on the fuel. Dyno testing as well as one 20 minute session with a 0-5psi gauge taped to my windshield had convinced me that my fuel pressure stays constant. Ignorance may be bliss (or not) in my case. I will see I guess.
I might have resolved my current problem. Turns out there was fuel leaking around the base of one of the grose jets that would eventually result in that bowl overfilling. It also seems that running a lower fuel level in the bowls might be more stable. I have no idea why that would be, but.... I initially set the floats to 16mm per the FSM. This resulted in the fuel level sitting at about 2/3 up the window. I still had overfilling with the pump running and the engine not. I reset the floats to 18.5mm and the fuel level sits now at slightly below the centerline. In this condition, I have not had any bowl overfilling. I don't know yet if that is just coincidence, a real thing or a result of running a bunch of fuel through the brand new grose jets and "settling" them. I am heading to the track on Friday, so will hopefully learn something useful (and successful?).
I am also starting to think the occasional on-track problems may be related to fuel boiling in the bowls. That is another rabbit hole I need to start climbing out of.
Thanks as always for all the detailed information.
So regarding the fuel boiling issue. This is a thing and is probably caused by the carb/intake being directly over the headers. Also the fact that radiator air is hot on our cars.
I have seen several solutions/fixes applied. Charlie Clark and Brian Haupt run a 3" hose with an inline blower (12v marine bilge blower) that pulls air from outside the engine compartment and directs it on to the carb. Mostly there in the event of a black flag all that means a complete shut down followed by a race restart. But Charlie has indicated that his car would stumble on track in hot weather so I think he turns his blower on all the time. When the Runoffs were at Topeka, I got a chance to look under the hood on Tom Thrash's EP RX7 and he had an elaborate insulation and ducting setup that blew cold air on the carb and bottom of the air box. In fact the entire right side of the engine compartment was covered in silver reflective insulation to keep the heat under control. Tom was FAST so not a bad idea to do as he did.
I feel like the hood vents have helped me in this area and I have no inner fender panels behind the strut tower. But I do have some new accessory circuits set aside and might use one for a blower.
The "on-track" incidents seem to have all happened following a rapid stop, either a spin or a rapid stop at pit-in for a driver change. I am guessing that the engine compartment is heat soaked and with the quick stop there is not longer "cooling" air coming through the engine compartment. It seems like a "leisurely" trip into the pits for a driver change may give the engine compartment a chance to cool down a bit, so that the fuel doesn't boil. We previously had difficulty restarting the car following a driver change. It would restart, but sometimes required a push start. I installed the heat shield shown below. I just added the additional heat insulation to the top. Previously there was only some on the underside. When idling in the driveway, the header surface temp is about 600 degF and the top of the shield is about 130 degF.
I also have considered installing a bilge blower. I decided to see how the grose jets, additional insulation and more care to slow stops works before installing a separate blower though.
I looked into the fuel side of it a bit. Despite ethanol having a higher boiling point than the "average" gasoline, when mixed with gasoline, the effective boiling point of the mixture is reduced below that of the base gasoline. The worst mixture is about 10% ethanol, which is of course what is used just about everywhere in the U.S. 10% ethanol reduces the effective boiling point by 20-30 degF. "Winter" fuel also has a lower effective boiling point. Fuel injection is not really effected, because of the higher fuel supply pressure. The worst case is probably the Nikki carb that only wants about 2psi of fuel pressure ;-) If this doesn't all get resolved, I may need to switch to fuel injection :-0
Are the fuel lines insulated in the engine Is the compartment? Do you have fuel return line? Those things might help, especially a fuel return because it keeps the gas circulating all the time when the pumps are running.
Can you not get 100% gas in CA? The local Quick Trips and Caseys around me have it on some of the pumps in high and low octanes. Super spendy right now but it is what I run in the car and the generator.
An SCCA GTL guy with a 12A did one of those throttle body injection setups. He says it works great. He is on the GTL Facebook group.
Personally I would go to an IDA and choke it down to match your ports. They are set and forget and with a glass ball needle and seat are not as sensitive to higher fuel pressure levels.
The fuel lines are not insulated. That is definitely a to-do. I have the stock return system that is open and functioning. I did notice recently that my muffler is kind of close to the gas tank, so will put a heat shield there too. Vented hood got reinstalled yesterday.
Apparently no 100% gasoline is essentially unavailable in California since about 2010. Ethanol is not mandated, but due to oxygenation requirements, it apparently all ends up at about 10%. I am pretty sure that some race gas can be found without ethanol, but at 100 gallons per weekend and $15-$20 per gallon that probably isn't going to happen for me. To say nothing about trying to transport that much fuel from a race gas source to the track in an Astro van towing a 12' open trailer ;-).
For the time being, I guess I will keep a close eye on things and continue to improve "cooling" in the engine compartment. Weber or fuel injection will be my last ditch options. Well actually last ditch would be to get another Spec Miata. I didn't say that out loud here did I? :-0
I read "Spec Miata" but did not hear you say it. However, 100 GALLONS OF FUEL IN A WEEKEND is still ringing in my ears. JEEZ!
So the latest episode of Engine Masters is appropriate to this conversation. They used a carb'd 383 Chevy that makes 460HP to determine if fuel temperature impacts HP. They tested fuel at room temp (75F), heated fuel using an NO2 heater (140F) and fuel that was iced down (40F). The results were interesting.
There was a 7HP spread between hot fuel and cold fuel. More significantly, when testing the heated fuel they had issues with the fuel expanding in the secondary fuel bowl, blowing past the needle and seat and flooding the engine at high RPMs. They had a thermal imaging camera on the engine and in each test, the intake manifold cooled quickly during each dyno pull regardless of fuel temp. The also tested icing down the intake manifold (a drag racing trick) and it made no difference.
Based on this, I think you need to insulate the side of the fuel cell next to the muffler and should plan on covering fuel line with insulation in the engine compartment or any place it is close to a heat source. I also think that cooling the carb would be beneficial for pit stops because low engine speeds do not move allot of fuel through a carb. Which means that the fuel spends more time in the fuel bowls getting heat soaked before it is consumed. A real issue when the car is idling or when the car shut off for refueling.
Yeah. 100 gallons is a bunch, but that is for an enduro weekend with typically 7-8.5 hours of driving on Saturday and 7 hours on Sunday. I am guessing that Conekiller uses more than that, since if I remember right they have a carbed 13B that might also be ported.
I will definitely check out the Engine Masters episode. I really enjoy that show. I like to see actual data. Frequently comes out a lot different than "common wisdom".
I put in a couple hours of driving at Willow Springs (and 9 hours total to and from the track) yesterday. The carb was behaving fine, but the ambient temps were only in the low 80's. I did have a nice spin at the end of a 19 lap session that stalled the car. The car started, but a little harder than normal. I tried not to give it time to overheat and/or flood.
I agree with all your recommendations. I had already scoped out a spot for a 3" bilge blower (where the battery used to be). I can actually just use my current headlight circuit, since I don't plan on any night time enduros in the near future. I will shield/insulate the muffler rather than the fuel tank since it is more accessible. Insulating the fuel lines also makes sense and is easy.
A quick carb/fuel cooling update. I installed shielding on the muffler (to protect the fuel tank) and added insulation to the heat shield below the intake. In both spots I used 1/4" thick ceramic blanket and dimpled aluminum sheet. With the car fully warmed up (coolant 190, oil 180) and idling in the driveway I got the following temperatures: EGT - 1050 degF, header surface - 660 degF, top of insulated part of intake heat shield - 93, small uninsulated section of intake heat shield - 160, exhaust pipe into muffler - 210, muffler surface 80, exhaust tail pipe - 170.
The most important data point I think is reduction in temperature of the intake heat shield. It is nearly 70 degF cooler than it was before I insulated it. It seems likely that modification alone should eliminate any possibility of boiling in the carb bowls. Only time will tell though.
The 80 degF muffler surface is also interesting, especially since that was basically the temp of both the insulated and uninsulated surfaces. I think the muffler shell takes quite a while to heat up, because the exhaust is primarily going through the muffler in a single perforated tube (straight-through) without any exhaust flow directly on the shell. Still I am sure that a lot less heat will transfer into the fuel in the tank once the shell temperature reaches equilibrium.
Also installed the bilge blower where the battery normally is located and ran 3" ducting over to the carb. I hope this isn't needed, because it is both ugly and annoyingly loud (not that either of those have any standing at the track).
Yeah. 100 gallons is a bunch, but that is for an enduro weekend with typically 7-8.5 hours of driving on Saturday and 7 hours on Sunday. I am guessing that Conekiller uses more than that, since if I remember right they have a carbed 13B that might also be ported.
Carl
I just noticed this ...lol...
Yea, we use anywhere from 135 to 150 gallons per weekend depending on race length, whether we do a practice day Friday and how much we run without braking. Average is about 7 to 9/gph. Last year when it was 115 degrees during the race at P.I.R. we evaporated an extra gallon per hour.
A quick carb/fuel cooling update. I installed shielding on the muffler (to protect the fuel tank) and added insulation to the heat shield below the intake. In both spots I used 1/4" thick ceramic blanket and dimpled aluminum sheet. With the car fully warmed up (coolant 190, oil 180) and idling in the driveway I got the following temperatures: EGT - 1050 degF, header surface - 660 degF, top of insulated part of intake heat shield - 93, small uninsulated section of intake heat shield - 160, exhaust pipe into muffler - 210, muffler surface 80, exhaust tail pipe - 170.
The most important data point I think is reduction in temperature of the intake heat shield. It is nearly 70 degF cooler than it was before I insulated it. It seems likely that modification alone should eliminate any possibility of boiling in the carb bowls. Only time will tell though.
The 80 degF muffler surface is also interesting, especially since that was basically the temp of both the insulated and uninsulated surfaces. I think the muffler shell takes quite a while to heat up, because the exhaust is primarily going through the muffler in a single perforated tube (straight-through) without any exhaust flow directly on the shell. Still I am sure that a lot less heat will transfer into the fuel in the tank once the shell temperature reaches equilibrium.
Also installed the bilge blower where the battery normally is located and ran 3" ducting over to the carb. I hope this isn't needed, because it is both ugly and annoyingly loud (not that either of those have any standing at the track).
Thanks again for your input and recommendations.
Carl
We ended up putting wood sheets between the plastic bladder in the cell and the outer skin, wrapped the out side of the cell in reflective insulation, added thicker and bigger sheet aluminum heat shield between the exhaust and cell, wrapped the fuel line from the firewall to carb in insulation and installed a bigger, thicker heatshield under the carb. This weekend will be the first warm/hot weather race since all the upgrades but we're expecting things to be good.
We have two 55 gallon drums mounted in the trailer plus we fill 4 5 gallon race cans and fill the car's 22 gallon cell. We run the car on 87 octane pump gas and it's far cheaper near my house than any of the tracks we go to so I fill up and haul it in and hope not to get hit by a train...
We have two 55 gallon drums mounted in the trailer plus we fill 4 5 gallon race cans and fill the car's 22 gallon cell. We run the car on 87 octane pump gas and it's far cheaper near my house than any of the tracks we go to so I fill up and haul it in and hope not to get hit by a train...
This is me crossing endurance racing off of my list of things to do next.
When split between 4 drivers the cost per driver is probably similar to sprint racing...
Not counting fuel for the tow vehicle and the generator, I would struggle to burn more than 20 gallons at an SCCA Majors weekend. At the Runoffs I paid for 20 gallons of Sunoco 93 octane and ended up putting 5 gallons in the truck. I realize that there can be more driving during an endurance racing weekend. So, more gas gets burned per driver but the out of pocket for fuel is not the same even when divided by 4.
When LeMons was new and coming to the Midwest, several of us put together a business plan for the build and estimated racing costs. Most of us already had club racing cars and in the end, the value wasn't there for us. The biggest stumbling blocks were the division of labor and what to do with drivers that could not provide sweat equity. I salute anyone that can make this work with a consistent group of racers.
Not counting fuel for the tow vehicle and the generator, I would struggle to burn more than 20 gallons at an SCCA Majors weekend. At the Runoffs I paid for 20 gallons of Sunoco 93 octane and ended up putting 5 gallons in the truck. I realize that there can be more driving during an endurance racing weekend. So, more gas gets burned per driver but the out of pocket for fuel is not the same even when divided by 4.
When LeMons was new and coming to the Midwest, several of us put together a business plan for the build and estimated racing costs. Most of us already had club racing cars and in the end, the value wasn't there for us. The biggest stumbling blocks were the division of labor and what to do with drivers that could not provide sweat equity. I salute anyone that can make this work with a consistent group of racers.
That's understandable. I've been lucky enough to have a great group of guys with me that help spread both the labor and financial burden. Around here the club/sprint racing side of things is a mess. If I were running the car myself the dollar per mile of racing would be much higher so this works well for me and my team. If you feel like flying out to the PNW I'll have a seat for you
That's understandable. I've been lucky enough to have a great group of guys with me that help spread both the labor and financial burden. Around here the club/sprint racing side of things is a mess. If I were running the car myself the dollar per mile of racing would be much higher so this works well for me and my team. If you feel like flying out to the PNW I'll have a seat for you
You're offering me a ride? You clearly didn't watch my in car video! That is a cool offer
We ended up putting wood sheets between the plastic bladder in the cell and the outer skin, wrapped the out side of the cell in reflective insulation, added thicker and bigger sheet aluminum heat shield between the exhaust and cell, wrapped the fuel line from the firewall to carb in insulation and installed a bigger, thicker heatshield under the carb. This weekend will be the first warm/hot weather race since all the upgrades but we're expecting things to be good.
So, after racing last weekend in almost 100 degree ambient we had virtually zero heat/fuel related issues. Oil temps were a different story. On two pit stops the car stumbled into turn one after exiting pits but that was it. $th gear synchro exploded five hours in to a seven hour race on Saturday and something clutch/input shaft failed at the beginning of hour 8 on Sunday's 8 hour race.
05-14-22, 10:30 PM
