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Drove the s10 home today from the shop (25miles) runs like a champ I didn't really get on it to much but what little I did it will scream! Coolant temp stayed right below 210 the whole time I was pleased about that only have a few issues to work out I'll need some input on. It has a small delay when your cruising and give it some gas for just a second May be carb or timing haven't messed with the carb much, and it's Dieseling a little when I shut it down, I put 90 in it today and it hasn't helped yet
Original tune was 12*0-1000 ramp to 30* at 3000 then ramp to 33 at 4000 had a miss in the lower rpm so I changed to
12* at 0 ramp to 17* at 500 to 20* at 1000 ramp to 30 at 2000 then up to 34* at 4000
It does the same thing on both tunes as far as Dieseling, definitely idled better on the first tune now idle is high and I can't get it down with idle screw may be in the carb? Second tune made a big difference in the way it runs no more miss in the lower rpms just a slight hesitation (not a miss more like poor throttle response) when you apply throttle while cruising for just a second then smooths right up. First time I've tried tuning so any advice will be helpful
Holley 750
Edelbrock performer dual plane
241 heads home ported
Stock 5.3 bottom end
212/218 .556 .556 112lsa
4l80 and 3.73 rear.
Compression around 9.5
Try raising your timing at idle. I have mine around 24 and am going to go higher soon. It solved my dieseling and idled a lot cleaner. Hope this helps. Eric L
Im running a nearly identical motor and its very hard to find people running low compression engines/small cams that have done much experimenting.
Keep your second tune, it will be a fine starting point, but I would eliminate the ramp to 20 at idle, get it to 17 and flat line it up to 1000 rpm, then up from there. You don't want the timing fluctuating at idle. With that said, I think you have more of a carb tuning issue. These motors, especially with smaller cams pull tons of vacuum at idle and low throttle position and it translates into lean conditions while operating on the transition slot. All the carbs I have set up on mild motors like this needed a lot of tuning to nail down the low speed/cruise. Make sure your transition slots are set correctly and try not to stray too far using the idle speed screw, if you must-use timing to set the idle. My current combo will change rpm at idle about 75 rpm with 1 degree. I run about 6 or 7 degrees at idle, but total out around 18 with vacuum advance, but don't worry about MAP now.
What size squirters and what accelerator pump cam are you running? I would put at least a 35 nozzle in the primary. If we cant get rid of your stumble with accelerator pump work, we can go further.
Just for comparison, here is the motor in my regal im talking about.
Stock compression 5.3
Performer rpm
Quickfuel 650
TFS 216/220-560 on a 114
Last edited by Horsepwraddict; Sep 23, 2014 at 10:16 AM.
i'm around 11.3:1 compression and run 40* at idle (1k rpm)and drop it to 31* by 2k rpm. i really need to get into MAP tuning this thing. the more time i gave it at idle, the cooler it runs, the crisper it drives off of a stop and the less dieseling. it still diesels slightly but i figured out to just turn the truck off in gear then put it in park. i'm sort of on the edge for 93 pump fuel.
Thanks for the responses I do believe its in the carb tuning and I may sou d like an idiot but im not sure what size squirters ot accelerator pump is in it. It is a 750 vaccum secondaries that came on a gmpp 350ho engine that we put in our 71 c10 the carb was never ran before this. Can I find out all that stuff without taking the carb completely apart? Ive never did to much with carbs on cars but have been through many small engine carbs. I did change my timing to 12 at 0 then 20 at500-1000 and it seems to idle better.
Well after doing some research it appears that the 350ho came with a holley 670cfm street avenger carb so I was wrong on the 750 I think it will work out fine says 300-400hp on holleys web site im gonna look in the morning and verify that
That carb will work well on that motor. Look at the squirter, there will be a number stamped on it on the inside facing the middle of the carb. Don't hold me to it but I think that carb comes with a pretty small squirter stock, like a 28 or something.
I just stole this picture from google, the squirter is what the screw is going through with the screwdriver on it.
I have also heard of problems with the pump arm being an issue with these. You may have to bend it down to contact the cam better. Rather than me explaining I found this video.
+1 on the accelerator pump & primary squirters. Mine would go lean while dithering in 6th gear in order to maintain highway speed @ low engine RPM. Increasing the vacuum pump size & primary squirter size solved the issue. This was after we tried accelerator pump ramp rate, timing, compressing acc. arm spring;...etc. We also have a wide band. So, were able to see the initial lean condition & the resulting AFR after the fix.
For reference: Went from a 30cc pump to a 50cc pump including arm change. Went up 4 squirter sizes.
which numbers show what model it is ive tried punching them in and everything leads to a 670 also I looked at that squirter screw and mine is a phillips head and I dont see any number on it maybe I need to pull it out and look?
there should be no play, but you should still be able to wiggle the lever on the pump diaphragm side to side with very little resistance on it. You don't want the arm and spring pushing down on the lever at idle, your wasting pump shot like that.
Check for play first. If you have any, fix it and if you still have some stumble put bigger squirters in it.
Well heres what I found out, the red plastic arm on tge choke was hanging up causing the idle to go high also causing it to diesel when I shut it off. Also adjusted the air fuel and now its drives completely different smooth acceleration crisp throttle and idles perfect. Thanks for all the advice next will be a wide band to do some more tuning. Timing is at 24* 0-1000 ramp to 30 at 2000 and 34 at 4000 may have to back it off at idle seems like it wants to spin longer when its hot before it fires
Well heres what I found out, the red plastic arm on tge choke was hanging up causing the idle to go high also causing it to diesel when I shut it off.
You do know that the red arm is for your high idle @ start up, right? It's there to increase start up idle speed & will release when you stab the gas after warm up.
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