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Discussion Starter #1 (Edited)
First off, i'm new to this forum, so I figured i'd say hello.

i've got a Honda HT3813 that i've had since new, 1990 and absolutely love it

I ran it for about 12 years before putting it in mothballs and just recently took it out and have gone thru it getting it back in shape for full time service. In fact i like it so much, i just bought a clunker off egay to have for spare parts.

just finished changing the timing belt, wasn't a big deal as i used to mechanic back in the 60s & early 70s at Datsun/Nissan & BMW dealership.

Problem that's just surfaced, i was cutting the grass (about a 2 acre yard) and toward the end it started surging kind of oddly - kind of a sudden loss of power for maybe a 1/10th of a second where rpm drop off then it quickly comes back.

I had remembered seeing a couple of postings on orphaned chat threads that i'd googled back in the spring, about thrust washer/bushing svc bulletin for the hydrostat transmission honda apparently had put out, but for some reason google isn't pulling those same threads up again.

But any assist on this is appreciated - the surging occurs whether the LT is in gear and roll, with or without blades turning, and even if sitting still on level ground. It starts to surge about 2200 rpm and becomes real pronounced around 3000 - 3400 rpm. It sure sounds/feels like fuel or electric, and i can't imagine how a bushing in the transmission could cause it when the tractor is sitting still, but that drive shaft is live or solid connection with the flywheel.

I did check the governor adjustment, per the svc manual, and it was spot on.

some history on svc performed past few months -

1) new timing belt was just installed - i was real careful lining the cam sprocket mark with the witness mark on the head, the crank mark was about 45 degrees off, but that's the way it was when i pulled the housing cover off. The belt hadn't stretched that much or there wasn't enough play for it to jump a tooth or two and watching the piston thru the spark plug hole, i knew piston was at TDC while the crank's marker was showing it about 45 degrees off - i figure the little sprocket washer with the crankshaft's mark had to have been mis-applied during original assembly - and again, the surging didn't start untill the end of the 2.5 hour cut session. Surging also does not start until the engine is fully warmed up - while i didn't race it to full rpm while warming up, after a minute or two of running, i took it to 2000 rpm and no surge - until it reaches full operating temp.

2) changed the oil in the hydrostat transmission - per honda svc manual spec, used 10-40W motor oil

3) Valves were also adjusted (first time in 20 years, and boy did it make a difference idling - much much smoother now).

4) Cleaned the fuel filter (back flushed), and I've been running some Chevron Techron fuel injector cleaner thru the engine, adding a couple ounces to every fuel tank fill up, to clean out the carb - stuff does wonders on injectors and is meant to be added thru the tank. But i just noticed the float on the carb, from pictures on ebay, appears to be some sort of plastic/foam item so i'm thinking next item to check would be the carb float to see if the Chevron Techron might have melted or affected the float.

any ideas or suggestions on this would be sorely appreciated.

and i've got one tip i'll post in a second thread about the clutch delay that a lot of posters on this board have mentioned - it had me scratching my head until i picked up a svc manual
 

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I saved off a note that surge can be caused by the transmission, written by someone on another forum years ago. The note related to the 4514 and 4518 tractors but maybe the same problem you are experiencing.

The problems described for the Honda 4514 and 4518 are ones that I've had. The surging is usually corrected by replacing the worn yoke collar bushing, part number 91556-VD6-003. Honda Lawn Tractor service bulletin #15 from March 1992 "H4514/H4518 transmission surging" describes the repair and list .9 hrs flat rate time.
Hope this helps
 

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Discussion Starter #3
thanks - i have the honda tech svc phone number and will give them a call next week to see if they show a TSB for the 3813 transmission's yoke bushing

and i figure when i get back from PA, i'll check fuel pump flow rate and carb float
 

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Discussion Starter #4 (Edited)
Made some progress on the surge problem

decided to start with the fuel pump, check it's flow rate per the svc manual's spec

only took 1.5 hours plus to get rear seat, fenders and seat pan off, to find you need to remove the rear frame cross member to get to the fuel pump

did a flow rate on it, and when it pumped, it seemed to be pumping proper flow rate. but it was cutting out erratically - the electrical connection was real tight, so it's either in the pump or the pump relay is bad.

Fortunately i had a spare fuel pump i bought off the bay a few weeks back - installed it, and found the fuel line running from tank to the pump was leaking, so replaced it as well. And while i had it out, I back flushed the fuel filter - will have to pick up a new one sometime soon.

got it all back together, warmed it up and ran it up to full throttle. Surge is 70-80% gone - a slight surge is still there, but only dropping 20-30rpm and not as often. Also noticed I'm now hitting 3600 rpm vs 3400/3500 before.

by the time i was thru, it was a full 4 hours (4:00PM to 8:00Pm) - either i'm getting slower, which is probably the case, or it was far more than i'd given it credit for, time wise.

I've got a carb float due in - when that gets here, i'll pull carb and check it

suspect i'll find the rest of the surge in the carb - layin the engine over on it's side when i changed the timing belt probably moved some sediment at the bottom of the float bowl around, and then when i cranked the engine up after re-installing it, when the fuel pump was refilling the float bowl, it probably stirred up the loose sediment and let some work into the jet

as soon as i've finished the Chevron techron, i'll get some of that seafoam - i did a google on it, found some interesting reviews

only posting this in case it helps someone else
 

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Discussion Starter #5
problem fixed -

got the new float in and pulled carb off last nite, float looked good and height was correct (to the best i could measure with an old Rochester carb float guage) and carb appeared real clean inside. Hosed it out anyway with some aerosoal automotive mass air sensor cleaner, blew all orifices with compressed air, re-assembled, and when warmed up, the slight surge was still there

then for the hey of it, to make sure i didn't have a vacuum leak, I sprayed some clear lacquer on the intake manifold gasket between the manifold and carb insulator block and the gasket between the insulator & carb to temporarily seal any possible vacuum leaks - (sprayed the two at same time while carb was still mounted on manifold.

started up - NO SURGE - There must have been a small pinhole leak - we used to use clear silicone spray with engine running when we thought we had a manifold leak, but that wouldn't have worked on this intermittent surge as the silicone usually gets sucked thru or into the engine pretty quickly, so that was reason for lacquer, to give me a little longer "sealing" of the pinhole if there was one

anyway, when i pulled the engine, there were two fuel line support clamps secured under the nuts on the carb's manifold studs - i had loosened them to remove the clamps and leave the lines in the tractor's "engine bay" - must have dislodged the carb and created a tiny leak

have ordered replacement gaskets - but the honda is back to normal
 

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Gentlemen the 3813 has a manual transmission and not a hydrostat. The yoke bushing only applies to the hydrostat. That is if I'm reading things right.
 
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