H35 backfires

TBailey

TBailey

New Member
#1
#1
After rebuilding the engine because the piston rod broke, I just can't get this 3.5 HP tecumseh to run correctly.
I even just bought a brand new carb for it.
I got it to idle great.
I can even give it about half throttle and it's ok.
But as soon as I open it up all the way, it starts sputtering and backfiring.

Could I have the timing off?

I need some advice, I'm a new mechanic, and just don't know what to look for, but if someone can give me some troubleshooting tips, I would appreciate it.
 
oldfatguy

oldfatguy

Active Member
#4
#4
a few things to check,

1, flywheel key
2, cam timing marks line up
3, spark plug gap and if you have a good hot blue spark. put in a new plug to be sure
4, carb adjustment- main metering screw
5, was there any damage to the head or piston ? also did you check the crank to see if it's worn ? I had a Tecumseh that kept throwing rods because the crank was worn out
 
TBailey

TBailey

New Member
#5
#5
I thought I lined up the marks, but now I"m not so sure. I could have come out of alignment somehow before I bolted it all up.

It is an adjustable carb. It has 3 screws in it, one for idle adjustment, another on the side under the first which I am lead to believe is the idle fuel adjustment, then another under the bowl, which I am told is for fuel mixture.
I had a diaphragm carb, but replaced it with this new one.

I will check those other things as well, oldfatguy.

Thanks for all the advice.
I guess I'll tear it down again, make sure it all looks good, then put it together again very carefully.

:thumbsup:
 
M

mfire39

Member
#6
#6
The screw on the side (not on the throttle butterfly) is the idle mixture screw. The screw under the float bowl is your high speed mixture.. Once you confirm that your timing is good, I would run the engine up in rpm's to the point where it starts sputtering or backfiring, and adjust the high speed screw.
 
TBailey

TBailey

New Member
#8
#8
Ok, took all the great advice here and did it all.
Pulled the engine back apart, but wasn't able to see if I had the timing wrong.
I wasn't paying attention and when I pulled the side off, the other gear inside came with it, and I wasn't able to see what position it was in.
Anyways, I made sure to put it all back in and together correctly.
Cranked it up, and it ran great.
Put it back in place on the 3-wheeler, and seems to be running perfectly now.

Now that it is running, I am going to tear the thing down, sandblast it, and repaint it.
Maybe get some new tires. These are old and are cracking a bit.

Thanks everyone!

 
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