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HH100 idle down issue??


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#1 IamSherwood OFFLINE  

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Posted March 31, 2011 - 04:51 PM

Need a bit of help/input here please. I'm not much of a motor guy, but
trying to learn.
When I first got this 1968 MF10 running back in Jan. I new it wasn't right,
but had to move it. So now I'm getting around to getting it running
better.
Back then, I had to run with 1/2 choke to keep it at idle. High revs it was ok.
So I figured clean carb. Done that. Did the whole service nozzle deal.
I'm pretty sure I'm getting enough fuel to the low speed circuit, because when I
remove the carb, and tip it to the left, I'm getting lots of gas running out
of the vent to the right of the idle mixture screw.
Now when I start it cold, it idles ok, throttles up ok, but as it warms up, it
doesn't what to idle down, until about 30 seconds later, and then has problems idling.
So my thought it was lean at idle. Took another look at carb. Discovered the
flange on the carb that bolts to the the block was deformed. About a 1/32" bow.
Someone must have really reefed on those nuts.
I placed a sheet of emery paper on a flat surface, and leveled off the face of the flange.
Tested after reinstalling, by spraying combustible carb cleaner at the flange, and
throttle shaft. Couldn't really notice any difference. There is a bit of play in the throttle
shaft, but other ones I have are worse.
This is where I start throwing darts. Could it be a bad head gasket? I don't know.
I take the head off. Pics below.
It's hard to see in the pic, but it almost looks like someone took a knife to the
exhaust seat in the block, and the knife jumped as they tried to scrape
the seat.(on the back right side)
The other thing I noticed, is that as I spin it through the strokes, the exhaust
valve rises about 10-15 thou on either the compression, or power stroke(can't remember which one it was) It shouldn't, right?

So, am I looking in the right area regarding this idle down issue?
I hope the pics are clear enough that they might show evidence of something.
And, of course, where do I go from here? Thanks
Posted Image
Posted Image
Posted Image

#2 DH1 OFFLINE  

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Posted March 31, 2011 - 05:04 PM

A good clean up and lap job on the valves would be a start to make it run better without spending any money. It doesn't look that bad.
Looks like motor has been running lean lately as you say.
The exhaust valve opening a little bit on the compression stroke is the decompressor doing it's job, when the engine starts and speeds up it stops opening the valve.
To get a really good slow steady idle everything has to be working right, valves, carb, spark, any weakness shows up hear.
IMO
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#3 NUTNDUN OFFLINE  

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Posted March 31, 2011 - 05:27 PM

I agree with Doug. If you didn't notice an increase in engine speed when you used the carb spray around the intake and throttle shaft. Since you have the head off I would decarbonize it, do a lap job on the valves and put a new head gasket on. One thing to check though is make sure the head isn't warped and also do the proper torque values and sequence. The head gasket on my hh120 in my Massey MF12g was shot and that thing wouldn't hold a consistent idle to save it's butt. I pulled the head, cleaned off the carbon and put a new head gasket on and she runs like a top now other then burning a little oil. :D
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#4 IamSherwood OFFLINE  

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Posted March 31, 2011 - 05:33 PM

Thanks Doug.
I was thinkin a combination of a whole bunch of things, that have to be sorted out.
Head gasket from auto parts store?
I guess I'll have to educate myself on lapping.


I guess it's kinda hard to say, without having them in your hands, but should I be
replacing the valves while I'm in there?
And, as far as clean up, scaper, and some sort of solvent?

Edited by IamSherwood, April 01, 2011 - 06:43 AM.


#5 IamSherwood OFFLINE  

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Posted March 31, 2011 - 05:35 PM

I agree with Doug. If you didn't notice an increase in engine speed when you used the carb spray around the intake and throttle shaft. Since you have the head off I would decarbonize it, do a lap job on the valves and put a new head gasket on. One thing to check though is make sure the head isn't warped and also do the proper torque values and sequence. The head gasket on my hh120 in my Massey MF12g was shot and that thing wouldn't hold a consistent idle to save it's butt. I pulled the head, cleaned off the carbon and put a new head gasket on and she runs like a top now other then burning a little oil. :D


Yes, I was going to check the head for warp. Thanks

#6 broken2 OFFLINE  

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Posted March 31, 2011 - 06:08 PM

After you lap the valves make sure to check the valve clearance. Good luck
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#7 DH1 OFFLINE  

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Posted March 31, 2011 - 08:50 PM

To clean the carbon off what I use is a combination of bench grinder with wire wheel, angle grinder with cup style wire wheel, and a drill with 1" wire brush on it.
The head is easy bench grinder and the drill takes care of it and gets all the tight corners clean.

The rest what I do is rotate the engine so the piston is down, put some oil all around the outside edge of the piston, rotate the engine again till the piston is at the top TDC with both valves closed. The wipe off excess oil.
Then clean with the angle grinder everything, piston, block surface, heads of both valves till spotless and shiny, making sure the piston does not move down, keep it at the top.
Next rotate the engine to move the piston down a bit and clean the walls, rotate more clean again, keep rotating until there is nothing left from in between the piston and walls when the piston goes down. When the piston goes up the dirt goes up and when it goes down it will remain behind on the walls, try to get it all. Adding a bit more oil helps.

To lap the valves you have remove the keepers so there free, remove the valves and then you can use the bench grinder with a fine wire wheel and clean the rest of the valves, stems and under side of the head, I try not to clean more than whats needed to remove the carbon.
Put the valves back in and lap them, make sure there is some valve clearance or lapping won't work.
Reinstall the keepers, check clearances, and your done.

Pic show the result. 2 different engines, last 2 pic before and after.

66 MF10 064..jpg

Attached Thumbnails

  • HH 014.jpg
  • 66 MF10 059..jpg

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#8 IamSherwood OFFLINE  

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Posted April 02, 2011 - 07:39 AM

One thing to check though is make sure the head isn't warped and also do the proper torque values and sequence.


Since there is no such thing as perfect, what would one consider warpped.
What's tolerable?

#9 IamSherwood OFFLINE  

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Posted April 03, 2011 - 08:15 AM

Not any better.
Cleaned all carbon away. Lapped valves, checked clearance, Ok
I couldn't find a gasket within 2 hr drive, so I gave the old one (which looks good)
a spray paint job. Checked head for warp, as best as I could, with straight edge, and
laying on a flat surfuce, nothing that my eyes could see. Torqued head down in
proper sequence.
Same symptoms as before. If I crack open the throttle, and back off quickley, it's ok.
If I leave at high revs for 10 seconds or so' and then back off the throttle to idle, it won't
idle down for about 30 seconds.
While running this time, I noticed flucuation if I moved the throttle shaft front
to back that small amount it is slopy. I'm guessing about 10-15 thou slop.

I'm also starting to wonder if that undercut we put in the main nozzle isn't
deep enough. We just barely got rid of the threads.

I'm going to get that nozzle undercut a bit more. Try it.
Then bush the throttle shaft. try it.
If that doesn't do it, I'll put in the new head gasket once it arrives.

Anyone have any other thoughts?

#10 DH1 OFFLINE  

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Posted April 03, 2011 - 05:29 PM

Sound like you going about it the only way you can, eliminate all the possibility's till it's right.
Could always try another carb of a HH100 or 120 that you know has a good idle.

#11 IamSherwood OFFLINE  

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Posted April 03, 2011 - 05:40 PM

Sound like you going about it the only way you can, eliminate all the possibility's till it's right.
Could always try another carb of a HH100 or 120 that you know has a good idle.


Yeah, thought about trying the carb off the 12, but I'm happy finally with
how it's running, and don't want to mess with it.

I've got a few other 12/10 carbs, but they're in worse shape then what I'm
dealing with. I think I'll just go ahead with the plan.

#12 DH1 OFFLINE  

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Posted April 03, 2011 - 05:46 PM

I put a top throttle bushing in 1 carb once and that for me solved the poor idle I had.
When you get it to idle like this your getting close.:thumbs:


#13 KennyP ONLINE  

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Posted April 03, 2011 - 06:27 PM

This may sound silly, but what is an HH100?
KennyP

#14 DH1 OFFLINE  

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Posted April 03, 2011 - 06:31 PM

This may sound silly, but what is an HH100?
KennyP

10hp Tecumseh cast iron block motor, and there's no silly questions here.

#15 IamSherwood OFFLINE  

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Posted April 04, 2011 - 09:46 AM

[quote name='DH1']I put a top throttle bushing in 1 carb once and that for me solved the poor idle I had.
When you get it to idle like this your getting close.:thumbs:[QUOTE]

LOL, yeah that's pretty close to a good idle.

If I could ever get an engine to idle that good, I'd quit my job, and start
workin on motors for a living.:D

Edited by IamSherwood, April 04, 2011 - 10:05 AM.
typo





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