Kentetsu

Man, I was really hoping that a carb rebuild would fix this issue but no joy. Push the gas pedal about 80% of the way down and you get pretty good power, but if you go farther than that you get zero acceleration. You don't really lose anything, just don't go any faster (kind of holds steady and sounds funny).

I just finished the carb rebuild today and that did not fix it. Fuel filter is new. Timing is correct. Leading plugs are new, so is cap/rotor.

Driveability is excellent now that the rebuild is done. The AP was completely clogged and now that that is fixed it feels great. Idles right at about 800 smooth as silk. No apparent vacuum leaks. Engine will go easily to the redline if you don't go past about 80% throttle.

I'm lost here. Something inside the dizzy maybe? Weak fuel pump? I don't think its fuel pressure related because its the same in every gear, at any speed. Open to suggestions....

One other thing that's probably unrelated, I think I messed up on the choke linkage. Pulling the choke no longer closes the flap on the carb....

Thanks for your time and help!

Kentetsu

Brought it in to work tonight, and she's running fairly strong now (probably 80% or so). However, put it to the floor and she goes nowhere. Floor it at idle and she'll stall out.

When I changed the leading plugs, they were light tan and looked good (so not running rich?). New plugs made no difference either.

This is driving me buggy! I want my power back!!!

kenn_chan

is your linkage set correctly? did you keep vacumm or go to mechanicals? regardless which setup you are useing, if your linkages are not set properly, or if one of the linkages got bent while rebuilding it can casue a multitude of problems.

if you have vacumm secondaries and the linkage jams without opening the plates, yet accelerator pump is dumping gas, can casue a nasty stumble/no acceleration at wot. just some thoughts

ken

or you can do the same thing I told Misthael and jsut give it to me

Kentetsu

Well, I have the secondaries switched to mechanical. I verified proper opening both before, and after installation. I pinned the gas pedal to the floor and verified visually that the plates are all opening fully.

This is an issue that I had both before, and after, the rebuild. Very strange...

snake eyes<l><l>

sounds like a flooding problem, i would say try leaning it out in the driveway and floor it a few times in park to see if it wont die.

my .02
<l><l>

candyassmiler

i had something similar. i thought my timing was right as well, but it wasnt. i adjusted by ear, and it ran great afterward, at full throttle. not to mention i had the same mods, ie. mechanical secondaries.

Kentetsu

Yeah, I tried messing around with the timing a bit, but moving it anywhere from its current position produces a noticeable difference in performance. I'm sure that the timing is correct. Under the light, it holds steady right on the markings for both lead and trailing.

Thanks for the ideas, please keep them coming. The motor feels very strong and smooth, just that it wants to die out at wide open throttle. Very frustrating!

Kentetsu

Any chance that having the throttle cable adjusted too tightly could cause this? I did verify that everything is opening properly, but with the power loss at full throttle I'm wondering if something else might be coming into play here.

The dropoff is very consistent, and seems to happen at the same point in the throttle operation. It doesn't build up slowly, it happens all at once. Just a thought....

Kentetsu

Bump to the top for the dayshift...

I know that someone out there can tell me what's going on with this...Thanks!

Kentetsu

Bump again...

Tech_Greek

Somewhere I read something about the fuel pump being crapped out if it works at partial throttle but not at WOT...your choice to investigate!

I’m just a kid though, who knows if what I’m telling you is any good or not!

- Tech

Kentetsu

Dude, I think you're reading my mind. I was considering fuel pressure on the way into work tonight. Unfortunately, I'll have to wait until this weekend to pick up a pressure gauge and check it out.

The only hole I could find with this theory is the fact that for a couple of weeks I was running with the secondaries completely disconnected. Seems like it would have enough pressure to at least run the primaries at wide open throttle. I mean, she's putting down decent power now (with the secondaries hooked up).

Anyway, its the best idea so far. Thanks Tech!

Kentetsu

Well, I just had a realization that blows this theory to hell...

The carb feeds off of the float bowls, not fuel pressure. So, if a weak fuel pump was the issue I should be able to take her up to speed, coast for a bit to allow the pump to refill the bowls, then floor it and have good power.

Doesn't match up. This problem is consistent at all speeds, rpms, and gears.

Still open to any suggestions...

IanS

iTrader: (4)

Not related to your problem, but with your rats nest removal you can also remove the thing that the orange plug attaches to and plug the vac lines. A "less cluttered" nikki, is a happier nikki. Also can swap the top most piece of carb with one from an 81-83 and have that bypassed completely. I will take some pics of my carb out of car and post them. Probably do that today as I will be putting it back in.

Tech_Greek

Remove the orange can of death before your engine kills you in your sleep...

- Tech

Kentetsu

Thanks IanS, might as well get that done too then. Couldn't really hurt at this point...

slashdawg00110

Yeah, fuel pump issues normally show under load, not revving in the driveway.

I'm a little confused on exactly what the problem is. In the first post, you said you just don't get any response after pushing the pedal down 80% or so. IS it just that, or are you getting stumbling/hesitation/crap after that magic 80%? If it's just that you get no response after 80%, I'd look for something misadjusted or a cable binding. Maybe the throttle is wide open when the pedal is at 80%.

Kentetsu

Yeah, sorry if I was unclear. Once you go past the 80% mark she just kind of stumbles and mutters. If you're going 60 and then floor it, you will only maintain your speed (barely) rather than accelerate.

Just as a test, I gave the throttle cable a bunch of slack so that I wouldn't be able to reach that dead zone with the gas pedal. Then, I pinned the gas pedal to the floor with a 2x4 and looked into the carb. Primaries were open about 80% and primaries were at about 30%.

I don't know if that means anything to anyone, but thought I'd throw it out there anyway.

One more thing. Sitting in the drive way; when you floor it suddenly it will die. But if you let it get past that first gasp it will shoot right to the redline without any trouble. Going down the road she will also go to the redline, but slowly because you can't really floor it.

slashdawg00110

You said you unclogged the AP, but how good of a shot is the AP delivering?

Have you looked at the fuel filter? I didn't see anyone ask about it, but a dirty filter will cause problems at idle and while not under load.

Check out this article from sterling's website.

http://www.sterlingmetalworks.com/ni...eshooting.html

Kentetsu

Fuel filter has already been replaced. The AP is giving a really nice shot of juice, and that has corrected an earlier problem that I had with taking off from a dead stop.

I will do a volume test on the fuel pump just for the sake of positively elliminating that possibility. However, as I stated before, coasting down and then flooring it produces the exact same conditions. The coasting prior to flooring it should allow the bowls to refill enough so that I should at least have a momentary burst of acceleration.

I've already been through Sterling's excellent troubleshooting guide.

The most baffling part of this issue is it's consistency. There is never a time when the power is there once you go past the 80% mark on the gas pedal. It does not change with gear, rpm, or speed.

The exhaust never smells rich either, and the plugs that I took out this past weekend were a nice shade of tan. I will try to take some shots of them, and also will pull the new ones for some pics.

I keep coming back to two possibilities; either a problem with the linkage, or a clogged passage leading to the secondaries that was somehow not cleared up during the rebuild. Although I have watched the secondaries in action and (at least in my opinion) they seem to be shooting plenty of gas. I'll see if I can grab a pic of that as well.

I'm going to pull the top off of the carb again today, but I'm not really sure what to look for exactly. If someone can point me in the direction of what might be blocking a secondary circuit, I would really appreciate it. I'll try reading up on the carb this morning to get a clearer picture of what's going on.

Man, this is really bumming me out right now though. The car used to really scream! Squawk the tires in 2nd and 3rd even. Then I loaned it to my dad for a few weeks, and then it sat for a couple of months during the snowy season. When I went to get it out for the spring, it was flooded. And after I got it running again it came back to life with this problem. My dad said that it ran fine the whole time that he had been driving it. This sucks, I feel like I have a sick child on my hands and is really getting me down 'cause I can't seem to help her no matter what I do....

Kentetsu

Problem solved!!! Now she's screaming again like a good girl should....

Having never rebuilt a Nikki carb (or any other in the last 20 years) I was relying heavily on the instructions that came with the kit. Unfortunately, all it had was a blow up drawing that looked like it was a bad copy of a six year old's school project.

I feel like such a noob! Never realized where the main jets were hiding and ended up missing them completely during the rebuild. I discovered my error while studying the FSM last night, then spent the day going through the whole rebuild process all over again...

Good news is, I found that the front-side jets were both partially clogged with some type of sediment. After cleaning them up with a small rusty nail (just kidding, I used a toothpick) I put her all back together minus a bunch of stuff I didn't need on the car anymore (thanks for your suggestions IanS). Normally its a bad thing when you have left over parts on something like this!

Anyway, put the carb back on and she started right up. Took her around the block a few times and what a joy!!! Finally got to hear what that RB exhaust sounds like at wide open throttle!!!!! I'm sure that some of you out there know how happy I am right now.

Thanks for all the help and support...

slashdawg00110

Excellent news! I'll have to remember that one. It's a bit like having a clogged fuel filter. On a related note, did you check the screens in the inlet banjo bolts? If they're crushed like mine were, you can toss 'em. If you're worried about having a little extra protection, you can drop in a in-line filter just before the carb.