4 cycle Troy Bilt TB635EC trimmer stalls at full throttle

roody2333

LawnSite Bronze Member
Location
nj
neighbor's machine, I know Troy Bilt is possibly the worst brand but that's what they commonly sell in the big box stores.

It would start and then immediately die.
I cleaned the carb and got it to run good but it would die at full throttle.

I changed the oil. It hasn't been used upside down as an edger or stored upside down or something (has an edger attachment also) being a 4 cycle without oil slinger technology like the Hondas, that could cause problems but isn't the issue.

I don't have an ultrasonic cleaner and usually I can clean a carb and fix it if the carb is the problem, but I bought a new carb thinking that was the problem.

New carb and new fuel filter and it still stalls at full throttle.

Next I replaced all the lines with Tygon and it still stalls at full throttle.
All of a sudden the primer bulb wouldn't prime so I took the bulb apart to see if I could fix something but then it would not snap back together. I bought a new primer bulb.

New primer bulb but still same problem stalling at full throttle.

Primer bulb has 3 nipples.
I thought I got the lines mixed up when it first wasn't priming, but I tried 6 combinations and 5 of them will pump gas and let it run but then stalls at full throttle.

Come to think of it, I'll run it without a fuel filter to see if it helps but I never had a problem with the batch of new filters this one came from.

You can see I wrote out the primer bulb nipple combinations, one nipple is shorter as a reference.

"pink' just means the line with the pink string I tied around it. pink goes to the bottom of the carb.

'carb' goes to the top of the carb

'tank' goes to the gas tank but isn't the line with the fuel filter that actually takes the fuel, this 'tank' line is the one that just barely goes into the top of the tank.

Come to think of it, maybe something got mixed up with these lines, maybe the line with the fuel filter should attach to the carb somewhere else but I usually wouldn't mix these things up and I drew a diagram while having it all apart and waiting for a new carb. But I'll try different combinations of those in the meantime.

cold start, it may need the throttle open to start.
When it stalls out you can hear the clutch or something in that area opposite of the pull start, keep spinning which seems off, but the shaft does spin on the power head.

I have feeler gauges etc and usually don't bother going that deep into a small engine but trying to get this fixed if can.

thanks
 

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Hurryupelectric

LawnSite Silver Member
Location
Charleston
I’ve had to pull out small screens inside of carburetors before to fix the same problem. They clog and limit the flow of gas. I’m not especially savvy with carburetors but I’ll just throw it out there.
 
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roody2333

LawnSite Bronze Member
Location
nj
Waiting on reply form troy bilt if they can please tell me the configuration of which line goes to what. schematics don't show.
There's a lot of combinations with 3 lines going into the carb and 3 on the primer bulb and it's kinda a PITA to keep pulling and testing each.


I doubt I didn't mix something up but other than that, any other ideas as to why it would die @ full throttle, and the spinning clutch thing? thank you
 

Breezmeister

LawnSite Gold Member
Location
South Jersey
The 1st vid should help you figure out the fuel line issue.....The second vid will explain why you should put everything in a box and give it back to your neighbor......




.
 

Integrity-LC

LawnSite Member
Location
West Michigan
The 1st vid should help you figure out the fuel line issue.....The second vid will explain why you should put everything in a box and give it back to your neighbor......




.

These are without a doubt the worst trimmers Ive ever had experience with. My neighbor bought one brand new and it didn't make it through one season. It was a nightmare to start and never ran well when it did, I worked on it multiple times for him and could never get it dialed in. That tiny crank case with a splash of oil in it is just not ideal in a trimmer. Stihl got it right with the 4 stroke with pre-mix and having worked on a couple Stihl 4 mix's they are not nearly as complicated as this troy bilt.
 
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roody2333

LawnSite Bronze Member
Location
nj
thanks but that video doesn't actually say which line goes to which 3 primer bulb nipples.

I found this though, different model but is the same (same carb and primer bulb part #s)


assuming it's not a line cross up, and if I also remove the new fuel filter, any ideas why it would stall at full throttle?


yes TB is prolly the worst brand but most people don't know that.
At first I was going to have him just buy a new one and switch it in the box and return it and keep the new one, I wouldn't feel guilty about that because TB needs to make products that last much longer, I'd put a tag on the trimmer noting what's wrong with it and it'd arrive at their refurbishing center with a problem they've probably seen many times before - but this model is discontinued and the newer one isn't really the same as if I could just swap the shroud covers and fake it.


I ran a 4 cycle ryobi powerhead for many years professionally and it worked fantastically except when I would edge with it upside down it would sometimes burn clouds of smoke.

Only the true 4 cycle honda and husqvarna (honda engine) and I think dolmar/makita (unsure if stihls are true 4 cycle) have oil slinger technology which allows it to run in any position while being lubricated and without burning off oil. I made some long threads about those in the past. I have the 35cc honda and a 25cc husq (honda engine) and they are so well built never a problem.

Neighbor uses attachments and stick edger and has those parts already, otherwise I'd suggest a refurbished 4 cycle husqvarrna but then would need the edger also if doesn't want to edge with string trimmer, or suggest the ryobi 4 cycle which are often on ebay cheap as store returns and run like new with minimal repair but the attachment connection isn't the same for ryobi, this one has the same attachment coupling as honda, If I can't get this running, maybe he'll just buy a 2 cycle or electric compatible with these attachments, I'd suggest spend for the honda, it'll last forever and is a joy to use, Or one of the honda clones off ebay for dirt cheap but unsure if parts are available in case everything isn't the exact same as the hondas (throttle assembly etc like that.
 

Integrity-LC

LawnSite Member
Location
West Michigan
thanks but that video doesn't actually say which line goes to which 3 primer bulb nipples.

I found this though, different model but is the same (same carb and primer bulb part #s)


assuming it's not a line cross up, and if I also remove the new fuel filter, any ideas why it would stall at full throttle?


yes TB is prolly the worst brand but most people don't know that.
At first I was going to have him just buy a new one and switch it in the box and return it and keep the new one, I wouldn't feel guilty about that because TB needs to make products that last much longer, I'd put a tag on the trimmer noting what's wrong with it and it'd arrive at their refurbishing center with a problem they've probably seen many times before - but this model is discontinued and the newer one isn't really the same as if I could just swap the shroud covers and fake it.


I ran a 4 cycle ryobi powerhead for many years professionally and it worked fantastically except when I would edge with it upside down it would sometimes burn clouds of smoke.

Only the true 4 cycle honda and husqvarna (honda engine) and I think dolmar/makita (unsure if stihls are true 4 cycle) have oil slinger technology which allows it to run in any position while being lubricated and without burning off oil. I made some long threads about those in the past. I have the 35cc honda and a 25cc husq (honda engine) and they are so well built never a problem.

Neighbor uses attachments and stick edger and has those parts already, otherwise I'd suggest the ryobi 4 cycle which are often on ebay cheap as store returns and run like new with minimal repair but the attachment connection isn't the same for ryobi, this one has the same attachment type as honda, If I can't get this running, maybe he'll just buy a 2 cycle or electric compatable with these attachments, I'd suggest spend for the honda, it'll last forever and a joy to use, Or one of the honda clones off ebay for dirt cheap but unsure if parts are available in case everything isn't the exact same as the hondas (throttle assembly etc like that.


So anyway, one last shot, any ideas what to check why it's dying at full throttle assuming I have all the line connections right?


If you've eliminated fuel deliver issues I would look at mechanical. Pull the valve cover and check valve lash.

BTW, the Stihl 4 Mix is a 4 stroke engine, it just runs on a 50:1 mix to avoid the issues that you've listed with 4 stokes with a wet crank case.
 
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roody2333

LawnSite Bronze Member
Location
nj
In case this helps anyone googling same issue. I cleaned and even removed spark arrestor, removed the fuel filter completely (new one though but just for good measure) , new tygon lines, new carb, removed air filter, new gas, new oil, sprayed carb cleaner while running around rubber boot that carb connects to and all areas that shouldn't hear any rev changes (would mean a leak), Can confirm by the diagram that I had the lines correct, BTW with this 3 nipple design if you fill the gas all the way up which I usually do with other trimmers no problem, this one will not prime if full, so that might be why I had that issue originally, something with the backflow line that just barely goes into the tank gets plugged if too full.
Anyway, all the above checked out ok but still stalls at full throttle so yes it does seem to be a rocker valve spacing issue (or something else, it did have enough oil when I first looked at it which is good it wasn't ran w/o oil), and I'll adjust with feeler gauge.

there's so many problems with this troy bilt that even without adding T B to the google search for diagnosis , so many threads etc come up about these 4 cycle T Bs having problems, so even if I get it running good with valve adjustment I'll suggest neighbor gets a honda 4 cycle and can still use the same attachments that fit the TB (different than ryobi/toro boom clamp adjustment coupling attachments).


I'm guessing this model also uses valve spacing .003-.006 (AKA in mm is .076-.152) as the one in this video he fixes. Seems pretty simple. I have the feeler gauges from when I adjusted a toro timemaster but it wasn't the problem.


 
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roody2333

LawnSite Bronze Member
Location
nj
can't run it now, but the valves were very tight, I couldn't even get the thinnest feeler gauge in there that is like 3X thinner than the spec, and I tried checking with piston all the way up /mid/and low same thing and pried a tad o it with a flat screwdriver to see if could get it to wiggle w/o loosening the nut.
I read valves too small causes power loss and high heat but read nothing about it not reaching full RPM and most the info is about cars.

Will loosen them a tad and see how it goes.
 

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