TBI305Camaro

Ok here is my setup.

9C1 lo5 350ci
l98 cam
stock lo5 heads
holley street dominator intake
holley 670cfm street avenger
complete dual exhaust with longtubes

After I have been on it alittle stop real quick and kill it it usually diesels just alittle...now sometimes when just driving it diesels alittle. Seems like its gotten worse since its gotten alittle colder...
any ideas? timing isnt to high i only have like 6 degrees base.

fuel pressure is at 5psi, and idle in gar is 750 and in P or N slightly over 1k

Mark A Shields

How is your idle? If it's too high that's the cause.

Since you say the timing is fine.

99Hawk120

High idle speed, timing, and carbon deposits in the combustion chamber are the most common reasons.

Mark A Shields

With a brand new motor, I hope he doesn't have any build up.

99Hawk120

Where's he say the motor's new?

Mark A Shields

He didn't I don't think, I just know he has one, I didn't expect you to know.

brodyscamaro

try lowering your idle just a tad. my car idles at about 700 in park/neutral and about 550 in gear. makes it sound better lol

TransAm

What kind of gas are you putting in? My car acts up if i put anything less than 93 in it... (dieseling, spark knock and such)

TBI305Camaro

Yeah better not be carbon deposits....

Idle is at 750 in gear and 1000 in P or N

Only way i can lower it is to go with less FP or less timing...my idle screw isnt even touching my linkage and my fast idle screw is backed way out.

and i run 92-93 octane/.

Mark A Shields

1000 in P is too high.

racing_dude_17

Hey TBI305Camaro, Sorry but this a little off subject but imm building a 350 and I have the street dominator and i was wondering how you liked it, thanx

TBI305Camaro

I like it...looked like a real good manifold plus it has a idle - 7200rpm powerband so its all ill ever need. It TALL tho...i can barely fit a street dominator intake, 670 SA carb and any aircleaner under the hood...has to get a drop base.

the idle is kinda high but what can i do about it?

F-BIRD'88

If the car will run at that speed with the idle speed screw adjusted all the way out, There must be air entering the manifold some other way.
Probabily a vacuum leak.

Marshall89ws6

when i used to have the 305 it would idle at like 1600 after a cold start then go down to 1000 in p normally and anywhere from 500-700 range in d.

primer84z

youve got a vacuum leak. try screwing in your mixture screws all the way. if the car doesnt die, youve definitly got a vacuum leak.

TBI305Camaro

it will die if i do that....ive checked and i cant find a leak anywhere....

with 7psi fuel pressure it idled at 2500rpm....

TBI305Camaro

so where should i check for leaks at? I only have 3 vac lines hooked up...the manifold vaccum, advance from the distributer and the power brakes...ill grab some carb cleaner tomorrow and spray around the manifold and see if its the intake manifold itself.

90Formula-X-F

You need to fix the reason your Idle screw isn't touching. Idle speed is the reason in almost all cases of dieseling. Timing to fast can make the idle not go low enough... vacume leaks and linkage such as cruise control or throttle cable to tight now with carb change over. vacume leaks and timing cause the diesel because they jack up the idle speed.. carbon build up on a F-body ? Dam I hope you keeper cleanner than that.. a little pedal action to fix that.... hehe

Fix the idle screw problem.. thats where it lies

TBI305Camaro

I forgot that I swapped carbs!!

The idle screw was touching and I backed it off and its idling at 750 in P, N and D now....geez I forgot all about switching the carbs out because I thought it was messed up and idling at 2500rpm (to much fuel pressure).

Oh well all good now.

You guys think 10 degrees advance with the advance hooked up is enough for my motor? 92-93 octane with 9.6:1 compression. What you think?

90Formula-X-F

Depends.. on if there is vacume to the distributor at idle.. better if it's ported vacume but if you have 10 degrees with it hooked up and there is vacume there then you are way retarded on your timing. I'm thinking you should be running about 6 degrees with your advance disconnected. What kinda plugs are you running ?

TBI305Camaro

Im running those accel U-groove header plugs. I think I am running around 6 with the advance disconnected. The distributer is a brand new proform High performance HEI. Says its has a advance suitable for high performance.

I pulled the plugs yesterday and they still look perfect. None are fouled or anything. No ash or black so I do not think im running either to lean or too rich.

99Hawk120

If you're only getting 10* at idle that's kind of low... I'm running about 18* base + 18* vacuum... of course, I've probably got a lot bigger cam than you do.

Try bumping the timing up a tad... it can't hurt.

TBI305Camaro

Im only running the l98 cam so it isnt very big. Ill adjust the timing some more but I dont want to get knock....don't want to trash this engine just yet.

99Hawk120

When I had the computer in the car, it adjusted timing at idle to be 40 deg at idle. I'd suggest figuring out your mechanical advance curve exactly... IE, base timing of 6* at 600rpm, mechanical advance starts coming in at 800rpm, all in by 32* 3000rpm, so total mechanical advance would be 26*.

Honestly, you're not going to get knock from 40* of timing at cruise in MOST cases. Hell, I'd try manifold vacuum, but you may have to bump the base timing up a little so that it doesn't retard the timing too much coming off idle. I'll be the first to say my timing curve isn't optimized, but I'd be willing to bet i have like 45* advance at cruise and I don't have any knock.