Originally Posted by Muggydude (Post 11294809)

Yes. However, You might want to try a 2096ss pipe instead. It will be very similar, but with a little more power and run time. I love it on my plus 4c

Originally Posted by mjealey (Post 11271747)

Hey guys, I have a Plus-4btt that has been absolutely bullet proof and been running fine for about 4 straight weekends until yesterday. I am running A Werks #6 plug in it with the stock Mugen clutch with the same OFNA 086 pipe I have been running this combo for 2 months. I have about 4 gallons on it. I was 4 minutes into the second 5 minute qualifier. I really have not touched the needles besides an hour here and there on the HSN each weekend and no flameouts over the last 2 months. The track had a long stretch and we twist the motors pretty good but all of a sudden the thing will die as soon as I let off the gas at the end of the straight 4 minutes into the heat. Motor was running perfect, nice and crisp, and only about 255 when i temped it.

I richened the top up a little bit, set it down to get 1 last lap in, made the whole 40 sec. lap and once again at the end of the stretch same thing when I let off the gas it just dies.

Repleced the plug and richened the LSN and increased idle gap, did the same thing in the 3 heat except earlier and in the 1st lap. Only dies at the end of the straight from being wide open for a good 3 to 4 seconds and then letting off to make sweeper curve? Idles fine, sounds great but keeps dying? I did not check it at the track, but maybe guessing front bearing? Need to tear into it tonight or tomorrow any ideas? We tuned on it the whole 3rd qualifier and the same thing no matter what we did. Also tried a #5 (hot) plufg and still did it?

Any ideas besides bearing or what would cause it to die after wide open throttle would help?

Originally Posted by Maximo (Post 11271920)

check for dirt in the front bearing........ remove the bearing, pull the shields and do a rinse test on a white paper and see if any dirt flows out......Your at 4 gallons and my guess is your engine needs a little TLC..she probably has a little wear and tear that needs to be addressed...

Originally Posted by mjealey (Post 11272199)

Ok, the front bearing test failed for one. So I pulled it apart and it looked clean inside and the piston and sleeve look really good. Motor was still pretty difficult to turn over by hand. Clean as a whistle inside but I will pull the bearing tomorrow to see if any fine dirt has made its way in. I think the bearing leak had just started and relatively small.

Secondly, I get the bone head of the year award. I pulled off the air filter assembly and there was no venturi in it! I pulled it all off and cleaned everything and I guess forgot to put the 6.5 venturi back in it. That is the dumbest thing I have ever done. My problem was 2-fold. Front bearing starting to leak and a dumb #$% human error. It was tuned for 6.5 and didn't have it in there so no wonder it was lean. It was not lean bogging though and running great until it flamed once you let off the gas. Anyway, I need to get a bearing and replace it before this weekend. I think I should be good. I feel confident after looking at it everything is okay just a really dumb user error I will never make again!!!

New rule also. All my engines get new bearings no question asked every 2 gallons from here on out, maybe overkill but that is what I am doing.....

Originally Posted by mjealey (Post 11295899)

Well, with new bearing, 6.5 Venturi, new c6tgc plug, the motor still did the exact same thing. New bearing and did the bearing test and the idle is completely unchanged. Drop it on the track and the engine is rockin! Running 250 and dialed. Same thing, about 4 minutes into a run it just shuts off at the end of the straight. We richened the HSN, leaned LSN and still did it. Did the opposite and still did it. Idles all day is smooth and crisp and just shuts off. We took it apart, everything is pristine, motor has a ton of pinch. Very tough to turn over by hand when cold, still really tight when warm. We spent 45 minutes with it this weekend and it did it every time after 3 to 4 minutes or running it. As soon as you are full throttle and let off the gas at the end of the straight it immediately dies. HSN really rich, or really lean still did it. Same with the bottom. Any ideas? I am lost with a barely broken in Plus-4btt and have never had a problem with any of my engines like this?

Originally Posted by Maximo (Post 11295915)

did you block the vacuum return port ?

what glowplug ?

how many head shims ?

it is possible you have some sort of fitment issue in there somewhere..... one odd one I have sen is where the top of the sleeve has some deviations and it causes the sleeve/head button to lose seal once it is heat soaked....... Flat sanding/stoning the top of the sleeve can correct this issue......

Originally Posted by Aleq (Post 11295917)

Maybe you need to flush out your fuel delivery system, chek it for leaks.. Or even clean your pipe.. Build up can be the problem.

Originally Posted by mjealey (Post 11295899)

Well, with new bearing, 6.5 Venturi, new c6tgc plug, the motor still did the exact same thing. New bearing and did the bearing test and the idle is completely unchanged. Drop it on the track and the engine is rockin! Running 250 and dialed. Same thing, about 4 minutes into a run it just shuts off at the end of the straight. We richened the HSN, leaned LSN and still did it. Did the opposite and still did it. Idles all day is smooth and crisp and just shuts off. We took it apart, everything is pristine, motor has a ton of pinch. Very tough to turn over by hand when cold, still really tight when warm. We spent 45 minutes with it this weekend and it did it every time after 3 to 4 minutes or running it. As soon as you are full throttle and let off the gas at the end of the straight it immediately dies. HSN really rich, or really lean still did it. Same with the bottom. Any ideas? I am lost with a barely broken in Plus-4btt and have never had a problem with any of my engines like this?

Originally Posted by chopper82p (Post 11296111)

Ok, check your fuel tank and lines. If it happens 3 to 4 minutes every time, than it must be your fuel tank or lines.

Originally Posted by Eivind E (Post 11296774)

Well I had a similar problem today at the races.
My 21-4C was running allright in the first qualifying heat, everything was fine.
Then the second qualifying heat, it ran great "on the bench" while tuning, then in the warm up it ran great, and then four laps in it just stalled.
Third qualifying heat, replaced the plug, made sure to get it tuned properly, spent 10 minutes running it warm and all, then sure enough it was running great in the warm up, the first four laps it was awesome, and then it stalled and my mechanic couldn't barely get it running again.

In the seconds before it stalled, on both occasions, it seemed to all of a sudden go very rich, like it was very soft on power, just the kind of symptoms you get when an engine is really rich, soft in bottom, very "progressive" sort of throttle response.

My friend suggested that it could be a bearing issue?
I'm stumped for suggestions.
When cold, if I turn over the flywheel, it seems to have decent enough compression.