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carburetor adjustments

7K views 5 replies 3 participants last post by  jlee5683 
#1 ·
i have a 1987 2.2L engine, with a 6520 holley carburetor, and i have had some issues with it running properly. i recently bought a new carb, but it didnt have all of the electronic components, so i returned it. my truck seems to not have enough fuel going through the carburetor into the engine. for it to run properly, the choke has to basically be all the way closed, and it can only idle when it is pretty much closed. i have tried adjusting the fuel mixture with the mixture adjustment screw, but it only seems to make no difference or make it worse. i cleaned it about a year ago, and it has barely been used, because it has been sitting at my house, being worked on. suggestions?
 
#2 ·
A little thing I learned about Holley carbs


The first thing I would check would be the carb's float level. If it is acting like the engine is not getting fuel, then most likely, it's not.
Always start at the source (in this case, the gas tank) and follow the path of travel (the fuel lines) to verify there are no restrictions. If you have a clean filter and no blockages between the tank and the carb, then the next place to look is the amount of supply available in the bowl.
I have seen a couple times the float levels were too low, even though they are supposed to be set at the factory.
While I have been typing this I have been trying to remember if the "6250" has the typical Holley float adjustment setup. If it does it will only take about a half turn on the adjustment nut to tell if this is sending you in the right direction.
If this helps great, if not I can dig out my Holley carb manual to get the true specs for you.
 
#4 ·

The first thing I would check would be the carb's float level. If it is acting like the engine is not getting fuel, then most likely, it's not.
Always start at the source (in this case, the gas tank) and follow the path of travel (the fuel lines) to verify there are no restrictions. If you have a clean filter and no blockages between the tank and the carb, then the next place to look is the amount of supply available in the bowl.
I have seen a couple times the float levels were too low, even though they are supposed to be set at the factory.
While I have been typing this I have been trying to remember if the "6250" has the typical Holley float adjustment setup. If it does it will only take about a half turn on the adjustment nut to tell if this is sending you in the right direction.
If this helps great, if not I can dig out my Holley carb manual to get the true specs for you.
I took a quick look online to see what the float adjustment nut is, and I definitely do not have one. Also, I have cleared out the fuel lines with compressed air, when I pulled the tank. It has probably been about 8 months since I have replaced the fuel filter, and I had the truck running really well about 6 months ago when I took it to the carb shop, but then a rod bearing spun, so I had to rebuild the engine, and now I'm back to square one. I've checked the timing(ignition and valve) several times, and it still runs like crap. I haven't made any adjustments to the carb except the idle speed screw since I got it back from the carb shop. The I haven't checked fuel pressure since I had the carb taken in to the carb shop, but when I checked, it maintained a decent 6 psi with a fuel filter without a return line, and specs are 4.5-7 psi for fuel pressure.

I appreciate your help and hope I can get it back to life so I can be done with it.
 
#3 ·
Definitely follow jlee's system of diagnosis. Being carbureted you should also be able to check the fuel pump pressure with a cheap vacuum/pressure guage to verify fuel pump condition. Depending when the fuel filters been changed last it wouldn't hurt to put a new one in.
 
#5 ·
If the fuel pressures good and it will run decent with choke on, which indicates it is starving of fuel, then I would say its either incorrectly set float or blocked fuel passages in the carb. If the carb was just done by a carb shop I'd take it back to them.
 
#6 ·
It takes 3 things to make an engine run: Fuel, air, and spark!
If you have to take air away to make it run means air is being introduced to the combustion chamber from another source.
If i were working on that engine, i would get the engine cranked and perform the following test. Use an oily type aresol such as "p b blaster" to spray along all your intake manifold and carb base. The reason i say an oily spray, you said this is a fresh built engine which means if you use something like either you will more than likely be rebuilding the engine again, plus the oily spray has a slower and longer action giving you a little more time to find the leak.
I don't know why i didn't think of this the other day when i first answered your post.
 
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