Question:
When i crack open the thottle, i get a horrible bog untill i back off the throttle. Quick blasts to halfway, the tires will squeal and the car takes off. Sometimes will backfire through the carb when cracked to WOT. Vacuum at idle is between 6-8 in hg. Specs for the engine build can be found here: [URL= http://www.jasperengines.com/p... Chevy 350 Class II[/URL] .
Ive gone up from 28 shooter in the from to a 35, and in the back from 31 to a 37. All stock pump cams and accelerator pumps. Still have the hesitation, although its a little bit better.(I wont backfire through the carb anymore from what i can tell, but still doesnt move off the line @ WOT). Any ideas?
Answers:
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I own a shop, build a lot of 350's, and race a lot. The level of vacuum you have tells it all. You can jet around all you want, but until you resolve the bad vacuum leak, you will get no where. You can try adjusting the timing to get it in quicker, but the backfiring sounds an awful lot like a lobe worn off the cam shaft, bent pushrod, weak valve springs, or burned valve. Jasper engines are a little less than what I would reccomend using. There is a big difference between a rebuilt engine, and a re-manufactured engine. One has new parts, while the other has the same parts, and only the bad parts were replaced. You may have valve springs that have over 100,000 miles on them. If you didn't break the engine in properly for the first 20 minutes, then you have a cam shaft that is shot, and will have to be replaced. If you have trouble getting the carburetor to come in tune, I would also suspect you had a problem getting the idle speed to come down too. Have you got the wrong intake on the engine? A leak under the carburetor, or the intake gaskets will also do this. Try taking your timing to 10 degrees BTD, and see if that helps, if so then go to 12 degrees. You might also suspect the distributor has problems with the mechanical advance coming in too soon. Did you put a curve kit in it? If so, step back to a stronger spring set, and reset the timing to 10 degrees. A bad vacuum chamber on the distributor can also cause this problem. I would rule out other causes as the culprit, because it seems you have been all over with the carburetor, and still have a bog problem. A faulty accelerator pump can cause this too. The secondaries not coming in properly will be another place to look. It seems if you have not much vacuum, all kinds of problems will rear its ugly face, and this includes lazy secondaries in the carburetor. I think if you find the reason for the vacuum loss, then you will find the reason for the whole problem.Part 2:
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Setting the timing with a vacuum gage will work, that is if you wish to burn a hole in a piston. It will work on a stock engine, but this is why they made timing lights. One other thing I can think of that will cause your problem is; the wrong spark plugs, or them breaking down due to them sutting up from too much fuel. A lot of times, too much fuel can foul the plugs partially enough for it to bog, and pop out of the hole. At least my drag car will do that when the plugs needs changed. I can install a new set, and it will come back to life. Check your heat range too.
Glad to help out, Good Luck!
Not enough info. It could be bad timing, or if you have a smog control pump, it may need replacement. Just guessing though.
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from what i can tell about it from what you have said,it may be off in the timing of it,this can make it do this a lot ,it only takes a few degrees to do this,even a little wear in the timing chain can cause this to happen,id start checking this stuff, i think the majority of it can be took out with the timing,good luck,i hope this help,s.91 gta just will not start,its that f---ing chip in the key,what can i do?
I think you may have a hole in the accelerator diaphram in your carb.How much would a 1995 toyota tacoma 4x4 be worth?
What manifold type do you have? If its an open plenum you are probably experiencing lag due to your cam and manifold combo is good for mid-hi range. A fix would be to get a performer RPM or equivalent dual plane intake manifold. This will help keep the fuel intake velocity up at low RPM and not hurt the hi end too much if at all. I've personally taken an Edelbrock Performer RPM on a 350 4bbl double pumper to 7,000 RPM with no hick-ups along the way. Otherwise try the 50cc accelerator pumps.where is the power steering filler on a 1995 nissan altima?
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Carb backfire is when the engine goes lean. 6-8 inch of vac is low. Either its got moderate compression and a big cam, or its got a vacuum leak, or the carb/ignition timing is way off.1992 Toyota Problem. Plz Help?
Make sure the ignition base and advance curve is correct. Shoot for 10* BTDC, and 32* at 3000. That'll get you in the ballpark.
Next, tune the carb. Which carb? You may need to make the shot last longer to give more fuel enrichment. You'll need to try a different pump cam and go down on the shooter size. Thats a big jump in shooter size for a 350. Doesn't mean much to have a big shooter if the cam isn't moving the lever at the right time.
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A 4150/4160 vacuum secondary carb in the 650-700 cfm range and the RPM dual-plane intake would work well. The RPM is hard to beat on street motors. If you've got a huge dual-feed double pumper with mechanical secondaries, they're harder to tune on a mid-sized engine on the street. Single plane intakes will cost you low-end and vacuum as well.
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You need to pick up the Holley tuner book that Haynes sells. I found mine at an auto parts place.
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check your timing dudeMore Questions & Answers ...
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