Tec H50 with Oval Bore Mikuni problem ... pics and Videos ...
Here is the pump I have and a bracket that came with it ..
But I don't have a pressure tap on my timing cover ....
The only thing open in the crank case is the breather ...
Is there somewhere else in the crank I can use?
I don't think I can just tap a hole, screw in a barb and connect the hose to it ... wouldn't the pulse area of the pump get oil in it?
Thoughts?
But I don't have a pressure tap on my timing cover ....
The only thing open in the crank case is the breather ...
Is there somewhere else in the crank I can use?
I don't think I can just tap a hole, screw in a barb and connect the hose to it ... wouldn't the pulse area of the pump get oil in it?
Thoughts?
The intake is the best place to mount. Tap it 1/8NPT and put a 1/4" barb there...with lots of JB Weld! :001_tt2: You will have no oil through the intake though...just fresh, clean, gasoline mixed air! If you mount the fuel pump high, the oil will drain back and you'll have no worries! if you decide to go that route
Well here's what I'm gonna do ...
The motor mounted tank was never intended to be the permanent tank.
I will zip tie another tank I have to the top frame rail, if that works then cool, if not then I will install the pump.
With the bobber seat that I intend to use, a small coffin type tank mounted on the top frame rail would look good with it .. (to me anyway)
I grabbed my 1/8" NPT tap and an "R" drill ... and a few brass fittings ... I'll play with it tomorrow.
The motor mounted tank was never intended to be the permanent tank.
I will zip tie another tank I have to the top frame rail, if that works then cool, if not then I will install the pump.
With the bobber seat that I intend to use, a small coffin type tank mounted on the top frame rail would look good with it .. (to me anyway)
I grabbed my 1/8" NPT tap and an "R" drill ... and a few brass fittings ... I'll play with it tomorrow.
Sixpac440, if you are for sure your going to put a fuel pump on your bike, you want to makesure you install the correct pump. on that style carb they are not design for fuel pumps and are more for gravity feed. i believe the needle and seat can not hold back alot of fuel presure,but walbro does make a fuel pump that some of the go kart guys use with that carb and works good. turk brothers racing does sell the correct pump that will work for your carb, under $14 +shipping. if you do call them or for anybody else. tell them what carb you are using and they will send the correct pump. also i hat to say this and maybe you already decided on this? but that nelson muffler got to go........
engine really needs a header pipe.:thumbsup: just may help tune that engine better.
nothing to do with your carb/pump issue, kind of curious if you ever check what the timing was on that and where tecumseh motorsports recommends where it needs to be and did you get any info on the cam spec'sfor that engine?
some guy on here that makes cool looking (old school) steel gas tanks. just trying to remember who?
AND YES,,,intake:thumbsup:
engine really needs a header pipe.:thumbsup: just may help tune that engine better.
nothing to do with your carb/pump issue, kind of curious if you ever check what the timing was on that and where tecumseh motorsports recommends where it needs to be and did you get any info on the cam spec'sfor that engine?
some guy on here that makes cool looking (old school) steel gas tanks. just trying to remember who?
AND YES,,,intake:thumbsup:
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I'm hoping the tank mounted on the frame rail (my end game plan) will take care of the fuel issue.
ole4 has said that Mikuni makes a needle and seat to work with a pump if flooding is an issue ... I suspect a Mikuni specific pump would be good correction as well if needed.
Yes, the Nelson is not a permanent exhaust. I will make something suited to the overall look. HOWEVER I do not want a screaming loud mini bike ... I will sacrifice performance if needed.
I will likely make a flange, weld up some 1-1/4" or 1-1/2" tube, run it down to the jack shaft then back to the left side by the rear tire keeping it at or above the frame rail. Is there a baffle or slip-on that will fit? Visual is important.
I will likely make a separate post on this to cast a wider net for ideas.
To the best of my knowledge the ignition and cam timing are non-adjustable on the H50 motorsports engine, at least the 1994 version I have. I have no information on the cam, duration, lift, etc, nada amigo! I know it does not have the compression release that are on the bigger Tecumsehs. It just has the dot to line it up with the crank. The crank and its gear are one piece.
As far as the intake ... for better or worse I made my own ...
https://www.oldminibikes.com/forum/projects-and-rides/143608-dorothy-heald-vt-7-goes-project-2.html#post1121278
No one threw up any red flags so I think it isn't the problem.
I'm not sure what I can do for a permanent tank, I will see where the triple tree comes to when locked at the ends of its travel.
But post up tank pics if you have ideas!!
I'm not hell bent on making one, buying another mans (or womans) art works too!
On the plus side this build is not a race with a deadline or a budget, this is 100% about the journey. It will be done when it feels right.
And thanks to everyone who puts in their 2 cents ... I don't always respond but it all gets read and digested!
Kevin
ole4 has said that Mikuni makes a needle and seat to work with a pump if flooding is an issue ... I suspect a Mikuni specific pump would be good correction as well if needed.
Yes, the Nelson is not a permanent exhaust. I will make something suited to the overall look. HOWEVER I do not want a screaming loud mini bike ... I will sacrifice performance if needed.
I will likely make a flange, weld up some 1-1/4" or 1-1/2" tube, run it down to the jack shaft then back to the left side by the rear tire keeping it at or above the frame rail. Is there a baffle or slip-on that will fit? Visual is important.
I will likely make a separate post on this to cast a wider net for ideas.
To the best of my knowledge the ignition and cam timing are non-adjustable on the H50 motorsports engine, at least the 1994 version I have. I have no information on the cam, duration, lift, etc, nada amigo! I know it does not have the compression release that are on the bigger Tecumsehs. It just has the dot to line it up with the crank. The crank and its gear are one piece.
As far as the intake ... for better or worse I made my own ...
https://www.oldminibikes.com/forum/projects-and-rides/143608-dorothy-heald-vt-7-goes-project-2.html#post1121278
No one threw up any red flags so I think it isn't the problem.
I'm not sure what I can do for a permanent tank, I will see where the triple tree comes to when locked at the ends of its travel.
But post up tank pics if you have ideas!!
I'm not hell bent on making one, buying another mans (or womans) art works too!
On the plus side this build is not a race with a deadline or a budget, this is 100% about the journey. It will be done when it feels right.
And thanks to everyone who puts in their 2 cents ... I don't always respond but it all gets read and digested!
Kevin
While my experience may pale in comparison to some of the guys who have posted, with some excellent ideas and theories, I agree that at high RPM you are fuel starving.
It seems as if you have the pump, jetting, and vacuum leaking aspects covered.
On a regular old Tecumseh, if I had this problem at max. governed speed, and the high speed jet didn't mitigate the problem, it WOULD be a misadjusted float setting. Or it'd be a tank vent problem.
So why is this any different? :smile: Because you are running a fuel pump? In my limited experience, I never overcame the float valve pressure with an intake-ported pump on a Chikuni. (Walbro pump)
If I were experiencing this high speed stutter, I'd remove the bowl and set the float higher, maybe even to the point where statically, I was venting fuel, just to test at high speed.
This would provide a quick indication to look somewhere else, and might even be the problem.
I was going to mention something about soak between the primary and secondary magneto coils, or plug or wire breakdown, but I'd ensure fuel flow was adequate first.
It seems as if you have the pump, jetting, and vacuum leaking aspects covered.
On a regular old Tecumseh, if I had this problem at max. governed speed, and the high speed jet didn't mitigate the problem, it WOULD be a misadjusted float setting. Or it'd be a tank vent problem.
So why is this any different? :smile: Because you are running a fuel pump? In my limited experience, I never overcame the float valve pressure with an intake-ported pump on a Chikuni. (Walbro pump)
If I were experiencing this high speed stutter, I'd remove the bowl and set the float higher, maybe even to the point where statically, I was venting fuel, just to test at high speed.
This would provide a quick indication to look somewhere else, and might even be the problem.
I was going to mention something about soak between the primary and secondary magneto coils, or plug or wire breakdown, but I'd ensure fuel flow was adequate first.
Put the other tank on and zip tied it to the frame rail above the Mikuni. The cap is vented.
All tests below were done using this tank mounted above the carb, not the motor mounded tank.
It performed the same.
In the vein of doing too much at once I changed the intake out to the one that came with the "kit", put in the #130 main Jet and replaced the Flex-jet with the one that came with the carb.
On a side note when removing the float bowl I was careful not to spill and gas .. here is a pic ... with the floats in the gas the level would be about right.
With the jet and intake changes it got up to 6600 and tho it was stuttering it was much milder and I was able to hold it WOT with no bog.
After some experimenting I found it runs best with the air cleaner off and the choke on but still wont go above 6600 ...
I don't know if this means anything but when it gets to 6000 or so there is a noise that builds through the max rpm, it sounds like a can of angry bees. Can a lean condition make noise?
At this point I'm wondering if the carb simply isn't too small for this application?
Runs best with choke (fuel enrichment) on and air cleaner off (more air).
It acts like it wants more fuel and air.
So I jury rigged the Tillotson in place using the "kit" intake and a string for the throttle.
This is a cantankerous carb that I have zero experience with, never got it dialed in but the motor stuttered at 5800/6000 and just ran really rough.
I didn't get much further as family stuff took over.
Also on the return trip to the house from testing in the neighborhood the #40 primary threw its master link for the 2nd time that day.
The clutches sprocket is getting chewed up by the chain ... I will check it out ... but I think I will be switching to a TAV for better control.
Kevin
All tests below were done using this tank mounted above the carb, not the motor mounded tank.
It performed the same.
In the vein of doing too much at once I changed the intake out to the one that came with the "kit", put in the #130 main Jet and replaced the Flex-jet with the one that came with the carb.
On a side note when removing the float bowl I was careful not to spill and gas .. here is a pic ... with the floats in the gas the level would be about right.
With the jet and intake changes it got up to 6600 and tho it was stuttering it was much milder and I was able to hold it WOT with no bog.
After some experimenting I found it runs best with the air cleaner off and the choke on but still wont go above 6600 ...
I don't know if this means anything but when it gets to 6000 or so there is a noise that builds through the max rpm, it sounds like a can of angry bees. Can a lean condition make noise?
At this point I'm wondering if the carb simply isn't too small for this application?
Runs best with choke (fuel enrichment) on and air cleaner off (more air).
It acts like it wants more fuel and air.
So I jury rigged the Tillotson in place using the "kit" intake and a string for the throttle.
This is a cantankerous carb that I have zero experience with, never got it dialed in but the motor stuttered at 5800/6000 and just ran really rough.
I didn't get much further as family stuff took over.
Also on the return trip to the house from testing in the neighborhood the #40 primary threw its master link for the 2nd time that day.
The clutches sprocket is getting chewed up by the chain ... I will check it out ... but I think I will be switching to a TAV for better control.
Kevin
I was hoping you'd tried moving the float up. Just because it's level doesn't mean you're not running out of fuel at high RPM. That was my point in the post above. Not that the floats were "misadjusted." But that the bowl volume was inadequate for the amount of fuel your engine requires above 6K.
Edit: Fuel level in float bowl statically is fine. (I see your photo) It's a question of where the fuel level is at 6K RPM.
Edit: Fuel level in float bowl statically is fine. (I see your photo) It's a question of where the fuel level is at 6K RPM.
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Kevin,
I really do not think you are going to like the Tillotson carb. Our experience with them is that they are a real pain in the ass to get tuned properly. Maybe they are great for WOT for racing at sustained high rpms, but for minibike riding where the rpm varies significantly all the way down to idle, they do not perform well - I'll never use another one. I would recommend staying with a Mikuni, even if you have to get another one.
Michael
I really do not think you are going to like the Tillotson carb. Our experience with them is that they are a real pain in the ass to get tuned properly. Maybe they are great for WOT for racing at sustained high rpms, but for minibike riding where the rpm varies significantly all the way down to idle, they do not perform well - I'll never use another one. I would recommend staying with a Mikuni, even if you have to get another one.
Michael
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.
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.