Tec H50 with Oval Bore Mikuni problem ... pics and Videos ...

[Sixpac440]

I will take my intake to work and check for leaks ... visually and a "mouth" vacuum test tell me its good.
With the 130 main, 17.5 Pilot, stock air jet and the "kit" intake it really hasn't run better, till it hits 6500.
With your conformation that this carb should be big enough for the motor, my focus is starting to move to electrical.
I talked to someone at ARC and they said the flywheel is good up to 7 grand but not much more.
I don't need to go to 7 grand, but the motor is supposed to do it so that's been my benchmark.
This bike is for trails, dirt, sand, hills, etc .. not balls to the wall street riding.

I'm having clutch issues and will be swapping it out for a TAV, I may not be bumping up against the 6500 RPM problem with a TAV as I wont need to spin it that fast to get my desired result.
The Mikuni setup when dialed in went to 6000RPM beautifully.

The Nelson exhaust will be going. I want to make a pipe and put a slip-on type muffler. The Kart muffler may be what's needed ... I will look into that more a little later after I get the TAV in place.

Kevin

These are my thoughts the carb will more than handle that motor . I have the same carb on a slightly modded Briggs flatty that's screams to 7500 , jets are a 125 main and 17.5 P . The 125 is to rich and fouls plugs after some racing laps , I just change to a new clean plug . The motor runs perfect and I don't want to touch it .
That said I also have another 22 mikuni that does the same thing on a clone that yours is doing falls off about 7600 and is lean . I have drilled jets up to 160 and the same .
This same carb last year on this same motor was dynoed and made 18.83 hp at 7700 and would go to 8500 no problem. So I either have a coil problem or vacuum leak .
I also build my own manifolds and will be really checking for leaks , mine are tig welded and are easy to see holes . I would really check your manifold closely.
Also with that exhaust that I saw there's no way that motor going to run 7 plus . Your going to need a proper header and a nonrestrictive kart style muffler.

 

[Sixpac440]

Checked the intake for leaks.
My buddy said use the Magnaflux kit ....

Easy to use, spray the red penetrant on the inside and the white developer on the outside ...

The 3 red spots on the outside were leaks. I welded and checked 3 more times till I got no leaks.

Kevin

 

[David wulf]

Kevin that mag kit is cool ass hell , where can I get one to test my manifolds ? Is it expensive ? The motor you have I heard can turn 7 plus .
The TEC Motorsports coil that's on it is a good one . I have that coil on my HS 50 with a billet rod and dyno cam , with a clone carb it would float the stock valve springs between 6800 and 6900 , strong damn motor . I'am putting it back together with a 10 over piston and I have that same Motorsports tilly carb you have and bigger springs .

 

[Sixpac440]

We have had that stuff in the shop for ages ... a quick Google search shows you can buy a kit or just the penetrant and developer.

So if I do buy another coil it should be the one I have?
The eBay seller I got the motor from has this one ... is it the same?
tecumseh ignition 36605k | eBay

Kevin

Kevin that mag kit is cool ass hell , where can I get one to test my manifolds ? Is it expensive ? The motor you have I heard can turn 7 plus .
The TEC Motorsports coil that's on it is a good one . I have that coil on my HS 50 with a billet rod and dyno cam , with a clone carb it would float the stock valve springs between 6800 and 6900 , strong damn motor . I'am putting it back together with a 10 over piston and I have that same Motorsports tilly carb you have and bigger springs .

 

[ole4]

yes same coil and it works on most of the h and hs series external magnet ignitions. It also make my hs50 run much better although I have never revved it over 5500 rpm as I am scared of that big cast iron flywheel. By the way what did you gap the coil at?

 

[Sixpac440]

Cool, I just ordered one ...

I did not gap the coil .. it came bolted in place, very close to the flywheel but not touching it.
It was making spark so I didn't think much more of it ...

What should it be?

yes same coil and it works on most of the h and hs series external magnet ignitions. It also make my hs50 run much better although I have never revved it over 5500 rpm as I am scared of that big cast iron flywheel. By the way what did you gap the coil at?

 

[ole4]

Rod Bolts-----150 inch lbs
Rod clearance-----.0035/.004
Piston to wall-----.005/.006
lash-----.008 depends on camshaft
Head bolts-----12.5 ft.lbs
Cover bolts-----100 inch lbs
Oil-----FHS 62R or Cramac Heavy
450 CHT
6500 on Cast rod
8500 on Billet rod
Stock flywheel key
40 ft.lbs on crank end bolt max


Safty Notes:
....... DO NOT alter flywheel
....... Use additional throttle return spring
....... Use race intended exhaust muffler
....... Use ignition saftey ground shut off switch
....... Vent crankcase into catch can
....... Always use clutch-chain guards

TECUMSEH H50 SERIES MOTORSPORT ENGINE SPECS
From what I remember it was big around .0125 coil to magnet air gap

 

[jaimenv]

Yea take that muffler off and try it.

Seriously, you have great intake with a restricted exhaust.

Another thing how about the spark plug gap, I would close it a bit if it still does the same thing after taking the muffler off.

good luck.

Jaime


PS Me in your shoes, I take that engine down and go over it, new/factory assembly don't mean a thing, specially if it says made in china. :wink:

 

[Sixpac440]

Copied and pasted to a word Doc ..
I torqued the rod, head, flywheel and cover bolts to H50 Motorsports specs. (motor came some assembly required)
What is "450 CHT?
Rod and piston to wall are what they are ...

Under Safety Notes:
I need a suitable exhaust (working on that)
Gonna need a catch can by the looks of it ...

Coil was not checked but when the new one arrives I will install it as per spec.

Plugs are NGK and gapped at .030

Is there a better/prefered plug and/or gap setting?

Rod Bolts-----150 inch lbs
Rod clearance-----.0035/.004
Piston to wall-----.005/.006
lash-----.008 depends on camshaft
Head bolts-----12.5 ft.lbs
Cover bolts-----100 inch lbs
Oil-----FHS 62R or Cramac Heavy
450 CHT
6500 on Cast rod
8500 on Billet rod
Stock flywheel key
40 ft.lbs on crank end bolt max


Safty Notes:
....... DO NOT alter flywheel
....... Use additional throttle return spring
....... Use race intended exhaust muffler
....... Use ignition saftey ground shut off switch
....... Vent crankcase into catch can
....... Always use clutch-chain guards

TECUMSEH H50 SERIES MOTORSPORT ENGINE SPECS
From what I remember it was big around .0125 coil to magnet air gap

 

[ole4]

CHT is heat temperature measured by a Plug mounted thermocouple. Try gaping your CDI to .0125. See if it changes anything.

 

[jaimenv]

Get it off the ground and run it

This way you will be able to see something happening that is difficult to see while test riding it.

I get mine off the ground on top of a wooden box and let er rip and observe and check for proper operation.

Chance this will at least help you figure out the chain sprocket problem.

Jaime

 

[Sixpac440]

Ok, got out there today with a cobbled exhaust ... made some changes but in the end it still stutters at 6000 to 6500 ...

Here's the exhaust ...
[video=youtube;WPz4EBnKEiQ]https://www.youtube.com/watch?v=WPz4EBnKEiQ&feature=youtu.be[/video]

The Mikuni is back on with the intake sealed up.
Jets are still 130 & 17.5
I used the tank on the motor but filled it to the top so the gas level is way above the float bowl.

With or without the exhaust spring, nothing.
Adjusted float level, nothing.
Tried different plugs, nothing.
Closed plug gap, nothing.
Moved the clip in the pin down 1, nothing.

Right now I'm leaning with either an electrical problem, it needs the fuel pump or the carb is just a lemon.
I will work on electrical first. I have a new magneto coming, it will get gapped correctly with a new plug.

Forgot to add:
With the bike on a stand I twist the throttle till it stumbles and it spits gas on my fingers from the back of the carb ....

And the beat goes on .....

 

[Sixpac440]

The primary chain is getting replaced with a TAV ... but for now I put the master link on so the clip is to the inside .. that should work for now ....

This way you will be able to see something happening that is difficult to see while test riding it.

I get mine off the ground on top of a wooden box and let er rip and observe and check for proper operation.

Chance this will at least help you figure out the chain sprocket problem.

Jaime

 

[ole4]

Please clarify spitting from back of carb?

 

[Sixpac440]

Please clarify spitting from back of carb?

With the bike on the stand in the garage, air cleaner off, the motor starts stumbling at high RPM, with my hand near the intake of the carb, maybe an inch away as it stutters my fingers get wet with gas spitting back out the intake of the carb.

 

[David wulf]

Do you have smaller jets ? My Briggs on the Powell is slightly modded and runs a 125 jet which is to rich for the motor . It does foul the plug and I just put a new one in . It use now is my flat track bike and after 20 min or so of time I put in a new plug . You ask why don't I jet it down , cause it screams on the big end and I like it that way . So back to your issue , drop down a size or two . There's no way that H 50 needs to fuel that my Briggs does .

 

[ole4]

That is reversion. You should be able to see a small loud by the mouth of the carb. What happens is fuel air goes out of carb then back in again picking up more fuel causing a overly rich mixture and the stumble. You may need to shorten manifold length. Or try longer exhaust but it will probably require intake change. Longer intake will lower reversion rpm shorter increase it. To be certain it is a reversion issue run it up and let it stumble look for a cloud or mist at mouth of carb. Then shut off and check the plug it should be black.

 

[jaimenv]

Correct me if I am wrong, but that fuel spitting out the carb sounds like a valve float symptom to me.

 

[Sixpac440]

Yes there is a cloud and the plug tho not black/black was well beyond tan ... this is also a well used plug.

I need to shorten the intake ... hmmm ...

That is reversion. You should be able to see a small loud by the mouth of the carb. What happens is fuel air goes out of carb then back in again picking up more fuel causing a overly rich mixture and the stumble. You may need to shorten manifold length. Or try longer exhaust but it will probably require intake change. Longer intake will lower reversion rpm shorter increase it. To be certain it is a reversion issue run it up and let it stumble look for a cloud or mist at mouth of carb. Then shut off and check the plug it should be black.

 

[ole4]

Didnt it come with A aluminum carb adapter about 5/8 ths inch thi k?