Need help getting my ht75 running right

[boutselis]

Has new fuel lines and carb re build.

It will start (a little hard) and will idol fine and run ok other than seeming a little rich but its the type of carb with only one jet screw and it doesn't seem to help.



Until it gets warmed up. then it stops idling and is very hard to get started again. It will die sometimes while its opened up.

Is that a crank seal problem?

 

[RiverRat2]

Has new fuel lines and carb re build.

It will start (a little hard) and will idol fine and run ok other than seeming a little rich but its the type of carb with only one jet screw and it doesn't seem to help.



Until it gets warmed up. then it stops idling and is very hard to get started again. It will die sometimes while its opened up.

Is that a crank seal problem?

I dont think so most leaky crank seals usually wont idle adjust at all,,,, real irratic but they usually keep running.....

It will be tough to adjust with the single ajustment carb

 

[fearofpavement]

Sounds like its running too rich and flooding. Air filter clean? Choke open?

 

[RiverRat2]

Check the compression Cold and hot an see what you get

 

[1steve]

Check the muffler screen if clear pull muffler and check for carbon clogging the exhaust port.

 

[boutselis]

Check the compression Cold and hot an see what you get

Compression hot was 120. I will have to morning to find out cold.

 

[boutselis]

Check the muffler screen if clear pull muffler and check for carbon clogging the exhaust port.

Believe it or not there was no screen on the muffler and no way to take off the exhaust deflector to look inside.

There was carbon build up arund the exhaust port of 1/16" in thickness all the way around. Removing it didn't help.

 

[boutselis]

Sounds like its running too rich and flooding. Air filter clean? Choke open?

Yes it is running to rich but wouldn't it flood pretty quick. I started it and let it idol and from the cold start to the time it started acting up was 1.5 to 2 minutes. (I'm just guessing at what the length of time seemed. I didn't time it) it seemed to act up just when it started to get hot.

 

[1steve]

Believe it or not there was no screen on the muffler and no way to take off the exhaust deflector to look inside.

There was carbon build up arund the exhaust port of 1/16" in thickness all the way around. Removing it didn't help.

So you did pull muffler?

 

[fearofpavement]

Yes it is running to rich but wouldn't it flood pretty quick. I started it and let it idol and from the cold start to the time it started acting up was 1.5 to 2 minutes. (I'm just guessing at what the length of time seemed. I didn't time it) it seemed to act up just when it started to get hot.

A cold engine needs more fuel to run. Hence the choke, primer, etc. As the engine warms up it needs less fuel and if it is getting too much it will flood out. So an overly rich mixture is less likely to be a problem when the engine is cold and more so when the engine is warm. That is probably why it starts hard when hot. One thing I would try is a new plug. ie, when it is hot and not wanting to start, put in a new plug and see if it fires right off. (I think it will)

What was the unit doing before you repaired the carb?

 

[nmurph]

are you sure you got the kit in the right order when you rebuilt the carb? i bought my 75 from a motorcycle mechanic who had recently rebuilt the carb. it would crank but not accelerate cleanly. i pulled it apart and sure enough he had reversed the gasket. put it back together and i runs like a charm.

 

[boutselis]

So you did pull muffler?

Yes. I pulled the muffler and removed carbon from the exhaust intake. piston and cylinder looks good.

A cold engine needs more fuel to run. Hence the choke, primer, etc. As the engine warms up it needs less fuel and if it is getting too much it will flood out. So an overly rich mixture is less likely to be a problem when the engine is cold and more so when the engine is warm. That is probably why it starts hard when hot. One thing I would try is a new plug. ie, when it is hot and not wanting to start, put in a new plug and see if it fires right off. (I think it will)

What was the unit doing before you repaired the carb?

Kinda the same thing it is doing now.

are you sure you got the kit in the right order when you rebuilt the carb? i bought my 75 from a motorcycle mechanic who had recently rebuilt the carb. it would crank but not accelerate cleanly. i pulled it apart and sure enough he had reversed the gasket. put it back together and i runs like a charm.

Yes the gasket and diaphrams are in the correct positions. I even checked that because I have put them in backwards before.

 

[boutselis]

I got it working. I took the carb off of my hs 80 hedge trimmer and that made it work much better. I still think its a little rich but this carb also has the one screw jet adjustment and it just won't lean up.. Must have been something in the stock carb but it is clean as a whistle so I don't know.


But in case anyone is interested the hs 80 hedge trimmer and the ht 75 (and probably 90 and 100) take almost the same exact carb.

 

[fishercat]

scrap the original carb.

they were junk. Go to the dealer and order the latest carb for the FS80 trimmer.

The mufflers were a little restricted as well. Opening them up a little won't hurt but don't go nuts.10-20% is good.

 

[nmurph]

I got it working. I took the carb off of my hs 80 hedge trimmer and that made it work much better. I still think its a little rich but this carb also has the one screw jet adjustment and it just won't lean up.. Must have been something in the stock carb but it is clean as a whistle so I don't know.


But in case anyone is interested the hs 80 hedge trimmer and the ht 75 (and probably 90 and 100) take almost the same exact carb.

i have an adjustable carb that will fit both. i was going to MM my polesaw, but i have never gotten around to it. i bought it from ebay for about $30. if anyone wants the PN, let me know. i can look on the packaging.

 

[Torquin]

i have an adjustable carb that will fit both. i was going to MM my polesaw, but i have never gotten around to it. i bought it from ebay for about $30. if anyone wants the PN, let me know. i can look on the packaging.

Yeah, I'm interested. I have an HT75 with what I'm guessing is a Zama carb on it, but that is only from searching the internet to see what carb is on it. I have not pulled anything apart yet, or cleaned anything. I am doing research before tackling the problem.
In my case, the HT75 starts and idles fine, but giving it more fuel is difficult. If I just pull the trigger all the way it cuts off immediately. It will eventually run full throttle if I pull the trigger very slowly. Ii have 2 adjustment screws, but neither makes any difference in how it runs. I was figuring on a rebuild or replacement of the carb, but I have only found rebuild kits for what I think is a Zama RB-66.

Thanks,
Chris

 

[nmurph]

I believe this is the Stihl PN-

4137-120-0614A

The carb body has s157 stamped on it, and when you look at the applications/cross reference page at Zamacarb.com http://zamacarb.com/pdfs/APPL_CR2011.pdf, that is the PN for the only carb that has 156 in the Zama item number.
I don't remember who gave me this as the replacement carb I needed for the polesaw, but I am pretty sure it was a Stihl dealer.

 

[Torquin]

Thanks for the info Murph. I found another post here that mentioned several carbs that would replace the HT75 carb:
"any of the carbs off of a fs75, 80, 85 should work the following C1Q-#S157, C1Q-#S69A, C1Q#-S80C, C1Q#-S63A, C1Q#-S78 are all fully adjustable", and found that the number you provided matches up with that post, so I will order one.

Thanks,
Chris

 

[dbittle]

HT 75 Carburetor

My saw came with the Zama C1Q-S137A. It has high, low and idle speed screws. New ones are on ebay at $50. Also, the Zama rebuild kit is RB-77. My local Stihl dealer wanted $40 for the kit although the place across town could order them for $15.

 

[Torquin]

I just bought a new one off Ebay, with the valuable info I learned here. Installed it and it runs like a new saw. The darn thing runs PERFECTLY!

Chris