Hi I have a 1980 f 700 or f800 not sure but it has the 370 engine in it. It runs bad very bad. found cylinder 3 4 and 7 are not fireing ive checked all the basics and it is kicking my butt. it has 160 psi comp, plug is black, swapped plugs, wires, and cap with known good parts, vac is low 17 but fairly steady and now im lost??

 

methinks some carb work is needed

 

well the carb that came on it was leaking fuel from sitting for a whyle so its got a newer carb that came off my mustang which has become my parts car, and it ran fine befor i parked it last fall so I would like to assume its good? but 4 of the plugs are golden brown one is dark brown and 3 are black?

 

did you use new plug wires?are they routed correctly so there not cross firing. check the dizzy cap for signs of carbon tracking both inside and out.also start her at night and watch for spark leaks

 

It has new wires new plugs new cap new rotor newer carb I even swaped the plugs and wires and cap (wouldnt be the 1st bad part out of box that ive got) . problem stayed in the same cylinders 3 4 and 7. I have a spark tester that goes in line and it lights up as bright as the cylinders that are working. it dosnt just pop once it pops alot. kinda reminds me of a rev limiter just its poping out the carb

 

Its 9:40 here so I just started it and it dose not have any leaky wires, it dose have the oe intake which had egr, but the hillbilly befor I got ahold of it blocked the egr off with a home made plate, and it dose have the duraspark set up still but I know verry little about them??????

 

it sounds like sticky valves maybe, but you say the compression is equal in all cylinders.

 

ya all 8 are from 157 to 161. which is one of the best that ive ever checked most are wider than that

 

check and see if you have bent pushrods first then i'd see if the cam was worn.you might try warming her up good and then flood her to a stop by dumping marvel mystery oil in her, then let her sit for a day.that might free up sticky valves if thats the problem.good luck

 

370's sometimes leak around the intake gasket and lean down certain cylinders. If you have good compression then mechanicaly the heads are OK.
Check for vacuum leaks ,also if you have vacuum boosted brakes the booster could be leaking or the resevoir or lines could be bad.

Have A Good Day-----------Hotwrench

 

good advice from hot wrench also check your firing order one more time

 

well I finally found it the brand new cam I put in has 11 out of 16 lobes worn off allready!!!!

 

Thanks alot for all the good tips, now what do I do with the cam? I bought the truck in boxes tore down the eng and found the oe cam worn down didnt think much of it it is a 1980 dump truck put back together and now it has wasted a nother cam ( truck hasnt ran more than 2 hours max and has 0 miles) Just bad luck? or something wrong???

 

did you put in new lifters with the cam.if you didnt thats a no no. also good cam lube and proper break in of the cam and lifters.dont forget to change the oil and filter.

 

Ya she got new cam new lifters new springs (stock but new) new valve seals, cam was just a cheap M Select but ive used these a few times with no problem, I started it set timing and ran it up to 1500 for 15 min per cam card with fress oil and filter, but it ran bad during break in?