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Too much fuel from accel. pump

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Old 03-13-18, 04:04 PM
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Where's my 10mm
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Too much fuel from accel. pump

Let's make this simple: If you want the whole story, read the entire bit below, if you just want the main question, read the second to last paragraph.

I just recently finished a total carb rebuild excluding jets, hoping it would fix any odd issues I was having regarding tuning. The car runs great now but it dies/bogs if you give it any gas under 2k rpm. Keep in mind this is under load only, out of gear you can rev all you want. The problem gets better the further out the accelerator pump link is screwed out, or in other words with less fuel. I do have to admit it seems that it's pushing a lot fuel out when you stomp the throttle so my theory is that somehow the accelerator pump is putting out too much fuel. This brings me to my second point. While rebuilding the carb I set the floats lower that "spec" according to the Haynes manual. It says 16mm from the gasket to the lowest point on the float when the air-horn is inverted. This looked a bit low so I set it closer to about 14 (they were even lower to start with). Later on I tried lowered the float even more, allowing more fuel into the bowls, which made the problem even worse.

I found a thread a while back while I was working on other carb stuff and it said the fuel should be in the middle of the sight glass at idle. If I had set the floats to spec (16mm), it would be well below that but keep in mind it runs better the closer to spec it is. At the moment, the accelerator pump link is unscrewed as far as it can go. I would have set the floats to spec by now but I'm wonder about fuel slosh around turns. So the question is 16mm or middle of sight glass? As a side note, at 16mm the floats barely moves down, not allowing the needles to move much if at all (the float droop setting is at spec).

Any help appreciated and a shout-out to everyone who has helped with the car previously (it's nearly done).
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Old 03-13-18, 08:56 PM
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Middle of sight glass is the proper result. Carbs are pressure-differential driven devices, and the height of the fuel in the bowl (and thus the mass of a fuel column level with it) is crucial to proper operation

Setting "dry" float measurements, both opening and closing, is a way to approximate the setting before reassembly, but it can be problematic as the points at which the measurement should be taken isn't precise - - the float corners are round, and so eyeballing it against the measure can be off a couple mm's. The thickness of the gasket (and you need to set it with the gasket in place) enters into it as well.

Whole point of the float setting is to automatically keep the bowl fuel level as close to the mid-glass hash marks as possible, under all operating conditions.
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Old 03-13-18, 09:10 PM
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ALWAYS at middle of sight glass,float levels never an issue til they're adjusted... i have never seen misadjusted floats on a Nikki-if i was 1st one opening carb up for repairs from when car was built in Japan.
Rebuilding a previously rebuilt carb,many times. Bottom line is the wet float level,and yes it's a pain to get them right-again. What was car doing that made carb overhaul necessary?

Did you use the replacement needles/seats from kit you used? Really shouldn't,they're all poorly made,all rebuild kits seem to come from same manufacturer.

IMHO any Haynes manual shouldn't be used for anything more than shimming a wobbly table leg. You can find fsm archived on this site. foxedca.rx7manuals. You'll find what you need there.
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Old 03-13-18, 11:28 PM
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1. The original reason for the rebuild was an unstable idle and flooding issues. That along with the fact that I bought the car after it had sit in a field for 16 years not running and it was just part if the resurrection.

2. Now that it's clear to go by the sight glasses, should it be the halfway mark at idle or just with the pump on, as the level drops just a hair while running.

3. Durring the rebuild I cleaned the carb thoroughly, used new gaskets (all but the ones for the vacuum plate), a new accelerator pump, check *****, and new valves and seats since the old ones kept getting stuck for no obvious reason.

Now the question is what could cause the accelerator pump to put out too much fuel? What things could be causing this and/or is it possible this same symptom could be caused by something else?
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Old 03-14-18, 08:46 AM
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Not, but is it possible to have installed the AC pump diaphragm backwards such that it pumps too much?

Also double check the air and fuel jets in the top of the carb body to make sure the right numbers are installed in the right holes. Don't ask me how I know this one.
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Old 03-14-18, 09:21 AM
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I don't think it's possible to install the AC pump backwards since the push rod that's attached to the diagram wouldn't fit. I had thought I installed the spring on wrong side though. It looks like the pump could have two springs, mine only has one and it's between the carb and diaphragm, not the diagram and back plate. Later today I'll check my SA carb (I've got an FB carb, intake, etc in the car right now) when I get home. It drove fine when it was installed so if it has two spings, I'll take one from my many part carbs. Do you know if they're supposed to have two springs? It would make sense since that would reduce stress on the diagram material, reduce how much fuel is present in the pump and also allow the adjustment linkage to varry a potential delay as opposed to just changing how much fuel is moved. Thoughts?
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Old 03-14-18, 10:46 AM
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Are you using an OEM fuel pump?

If no, have you checked the fuel pressure?

Your problem can be caused by excessive fuel pressure.

The Nikki wants between 3.7 to 4.7 psi.

Last edited by rwatson5651; 03-14-18 at 10:50 AM.
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Old 03-14-18, 10:59 AM
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It's the oem pump so....
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Old 03-14-18, 12:30 PM
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The Nikki only wants 2.5 psi.
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Old 03-14-18, 12:49 PM
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Just checked the RX-7 Carb FSM. There's no second spring so I guess that's out of the question. Could tuning (idle mixture and speed) cause the car to die every time you even touch the gas pedal? Anything else that could be culprit? Could the jets be messed up by the PO and that's causing the issue? I guess anything is possible... All ideas welcome.

Last edited by Benjamin4456; 03-14-18 at 12:55 PM.
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Old 03-16-18, 09:43 AM
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Well I found one small problem. Although it didn't fix anything obvious, there was a connector leading to the Ignition Control Module that was unplugged. Maybe that's why my vacuum advance wasn't getting a signal... Not sure, I haven't checked anything out yet. Next time I'll be able to work on it is next week.
On a different note I've come to the conclusion that the problem is something other than the AP unless it's really picky about how it's adjusted. I haven't gotten a chance to check the jets yet so I'll do that next week. During the rebuild I did change the smaller of the primary jets (excuse my lack of terminology) with ones from another carb as one of them had half of the top broken off. Maybe that caused a problem? I've gone through the entire rats nest and it doesn't seem there are any vacuum leaks so that's not it, I've replaced many of the lines with new ones. Timing is dead on and all plugs are firing. Is there anything else besides carb stuff that could cause a problem like this?

Last edited by Benjamin4456; 03-16-18 at 10:41 AM.
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