Problems With Idle

Alright. I finally got the Timing up to 16. She pulls hard now and has alot of power. But, it has a really weak idle and still won't stay running in gear. She just wants to choke an die when i put her in gear. When I say weak, i mean that when I have it in gear and am slightly pressing the pedal to keep it running, its kind of sputtering and feels like she'll die when I let go. It's so wierd. The motor Really hates to idle lower than 1000 rpms.
Also, It kind of chokes right off idle when i go to drive and more frequently will pop back through the carb and kill the motor. When i rev it up it won't ping like it's too adv.
I've adjusted the float levels and it doesn't seem to be running very rich at idle.

Is this cam just a bad choice for the motor? Thats the only thing i can come up with.

Besides the timing issue it sounds like there could be more then one thing going on here. Lets get back to this carb for a minute. Is it the street avanger 570 cfm ? Is it manual choke or electric choke? That is quite a bit under carbed for a 10-1 compression motor. And also are you possitive there is no vacume leak anywhere? What 280 cam and lifter combo do you have?

I run that Comp Cam 280/480 in my 327 with a Q-jet and it idles at 750 rpm just like a cat purring. The motor does not really come alive until around 1500 rpm but does not sputter off idle. Is your vacuum advance hooked up to your distributor and are you using full vacuum or ported vacuum. I use full vacuum which gives me alot of timing at idle which helps keep it running at idle. My mechanical advance starts to come in around 1200 rpm and in fully around 2800 rpm. Spend some quality time with your timing light and you will learn what your engine wants.
I have been told and I agree with that most perceived carb problems are actually timing problems.

The carb is a 570 street avenger elec. choke with new primary an secondary jets. 68 pri/ 74sec. I have the idle mixture screws at 1 1/2 turns. I'm running the vacuum line off the top side where it says to, not the full manifold. The cam is a comp 280 hyd flat. its 480int./480exh lift, advertised dur at 280/280, 110 sep ( http://www.summitracing.com/parts/CCA-CL12-212-2/ ) . I have stock lifters, 1.5:1. I'm fairly sure there isn't a vacuum leak, but i've already had to replace my intake gasket due to a vac leak. In that case, the idle would fluctuate really bad, its not doin that now.

What might you be thinking mooneye?

Guess i'm gonna have to look into messin with the timing alot more.

Seems like something with timing is still not quite right. It needs to be set at 16 initial without the vac. advance hooked up and the idle as low as it will possibly go to make sure no mechanical advance is coming in.

The carb could be a little lean for that cam, but shouldn't be that bad. Try backing the screws out a 1/2 turn more each.

The 280 cam shouldn't have a problem idling at 850 rpm. The off idle stumble may or may not be a carb problem. Have to get the timing positively squared away before tweaking the carb. But, most likely with that cam, the squirter nozzle and pump cam is going to have to be changed to make it crisp.

I did not get a good idle with ported vacuum to vacuum advance canister. Not enough timing at idle. I had to run FULL VACUUM to the vacuum advance canister to get it to idle. I run 12 degrees at the crank with the vacuum line plugged and 800 rpm. As I raise engine rpm to around 3000 rpm, I get timing of 32 degrees. I then plug in vacuum line and my timing goes to more than 20 degrees (not sure so I wont say) but when I raise engine rpm to around 3000 rpm, I get timing of 52 degrees.
http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf
http://www.lbfun.com/warehouse/tech_..._explained.pdf
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf
I've included a couple of links from Lars Grimsrud and the last link states if you have a radical cam and need more timing to get an acceptable idle, use manifold vacuum to your vacuum advance. I also changed my vacuum advance canister to the AR31 can and it made all the difference.
Read these links and do what Lars, Camaro, and I say and this will cure your motor.
Good luck and keep us posted.

Thanks for the articles 184. They helped out alot. I'll be messin with my timing later this weekend to see if I can get it running better.

My dad and brother seem to think that I may have stuffed the cam at 2 deg adv when I put it in. Might explain some problems, but i'm not sure.

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Originally Posted by Warpig7

Thanks for the articles 184. They helped out alot. I'll be messin with my timing later this weekend to see if I can get it running better.

My dad and brother seem to think that I may have stuffed the cam at 2 deg adv when I put it in. Might explain some problems, but i'm not sure.

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Even if you put it in 2 degrees advanced, it's not going to make that much difference. I normally run mine 4-6 degrees advanced.

I run my cams all over the place. If I don't like how it performs on the bottom in at 0, I'll advance it 4, 6, 7, etc... to see if it gets better. Normally, advancing helps bottom end and retarding helps top end. I've noticed a cam seems to lose power though the more you retard it in an engine.

Quote:

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Originally Posted by Warpig7

My dad and brother seem to think that I may have stuffed the cam at 2 deg adv when I put it in. Might explain some problems, but i'm not sure.

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All 2 deg adv means is you add 2 deg to the value you read at the crank. No big deal. I run mine at 4 deg adv. Besides, did you install the cam advanced or straight up. Were the dots straight or did you install advance bushings?

I installed it straight an didn't use any bushings. From messin around with it today, I feel that I just need to get the timing on and tune the Carb.

Here's where I'm at: I took the timing from 16 to 14 to see how it would react, It went back to sputtering at high rpm let off, it felt as though it lost power, but the off idle bump was more crisp. At 18 deg, it chokes right off idle alot more but picks up goes strong. It has noticeably more power. The idle is smoother at cold start-up and at 1000 rpm, under 1k it's really weak.

I noticed something new: I took off the vac adv and plugged the carb. Set the timing at 18 and ran the motor up to about 3k to see how it pulls timing. Then I plugged the vac adv into the Full Manifold port. When I went back to check timing, it hadn't pulled any additional timing, so I ran the motor up to about 3k to see how it pulls timing and it didn't seem to pull any faster than it did mechanically.

*Update
The vac adv diaphram on the dist is toast, I had to put in a different distributor. It pulls timing now. I checked the vacuum at idle, 8-9lbs. But, I had to set the timing at around 22 deg to get it to run right, then i put on the vac adv. The idle still won't go lower than 1k. I took it for a run and it pulled hard but when i let off the throttle at high rpm it would sputter, like before. I pulled timing down to around 18 and had ran to the store, when i went to start up, the starter could barely turn the motor and it ran like trash.

I'm thinkin that when i first set the dist the oil pump drive was off, causing the dist to be off. So I'm gonna set the engine to TDC and check it out.

Any suggestions? This is really kickin my butt

Coming to the party late here, but I had a similar problem a while back - ended up tracing it back to spark plugs - short reach plugs in long plug hole, probably were sparking outside the chamber :whacked:

I also had to set my initial timing way high like 16 or 18 degrees and the truck would not idle well below 1000 rpm but it made great driving power

Once I changed the plugs everything else fell back into place and I undid all the "fixes" I had previously attempted - now we all cool and all is at it should be. Don't overlook the little things and make sure your plug gaps are correct for your build and the same on all cyls.

Good catch on the bad vac adv on the dizzy :cool: