Batass

I took out my car the other day and it was blubbering past 4000 rpms. The AFR gauge was reading around 15 when it happens. When it ran fine previously the afr was about 11.7 WOT.

Plugs are new and gapped to .035
Base FP is 6 and rises with boost as much as I can tell free revving.

The only change made is a larger air filter but the car has been run without any filter so I don't think this is the problem.

It also ran great the few times I took it out over the winter, which should have been a more lean condition than a 70* day.

Maybe the carb got some crap in it, or the ignition is faulty? I do use a BTM...

I don't have much time to work on it and troubleshoot so I was wondering
any ideas?

Batass

I found that the pin that holds the duckbill vent in the bowl had come loose and had carbon around it. Must've blown loose during a backfire. It must have been bleeding off pressure from the float bowl and the secondaries weren't fueling.

5literTPIterror

im interested in this. but from whta i understand youre saying, my carb is doin the opposite.... under boost/wot the afr is good, but under part throttle/cruise the car breaks up some and runs sorta rough, and afr is in the high 9:1's, start to build boost and it smooths out and pulls hard and even.
ive jetted down the primaries and checked some obvious things and cant seem to get the part throttle break up to go away...... i think im down to 64's in the front for jets.......

- i also run a msd 6al btm, msd pro billet dist. and autolite 3922 plugs gapped at .030"

Batass

So you have a rich cruise? Whats idle like? What carb?

5literTPIterror

well i personally think that my innovate LM1 is a piece of garbage! i get all kinds of weird readings every now and then including lean spikes that shouldnt even be posssible.
like ill be driving along and all the sudden it'll go from a normal afr like 11:1 to like 20 or 21:1!!! then right back to normal.

my carb is a CSU 750 (holley 4150)

yes im expierencing rich cruise/part throttle (9.5-10.0:1) and it also breaks up and pops some under part throttle....
my idle i thnk is good...i think when i checked that it was ranging from 13 to 15:1,
like i said i cant stand that LM1, wish i had a different wideband altogether.

Batass

Well I don't perfectly recall how the cruise circuit works so I don't want to give you any false info, I'd make a new post about that.

I get the spikes sometimes too, but I think its because of a changing load on the engine, slight decel. I remember reading that your supposed to replace the sensor after 50 hours or something like that.

I like the LM1 but I think it should have come with the rpm cable and a smaller box. Its really just meant to be an easy reference or a good idea of conditions, plug reading is still very important since the LM1 can't read individual cylinders and thats usually how motors are ruined, by one or two cylinders.

5literTPIterror

i talked to Kevin at CSU yesterday and im gonna try to lean it out some with the mixture screws and try a new power valve and see how it goes.