Mikuni vents and starting issues

[Old Geezer]

I've just bought a brand new 38mm carby for my 85 500 (under $150 delivered) on advice from a Husky tuner for easier starting & is better suited for general riding, 40mm was really only good for high speed stuff apparently.
I've got it all hooked up using 430 intake & reeds & it runs great.
I use the lean it over method for cold starts.
Something I also saw is that you are using a 50 pilot, mine is a 40 & I was told the larger you go makes it harder to start.
Hope this helps,
Speedy

Speedy,

Can you tell me the jetting you're using with the 38mm on your 500? I will be swapping out the 40mm eventually for a 38, but I don't imagine the jetting should stay the same as what I currently have in the 40. Just looking for a baseline, and I can go from there.

I'm really struggling with finding a suitable sized rubber intake flange to mount a 38 to the reed block of my XC500. No problem finding the right carb intake dimension (43mm diameter) but it's the bolt spacing for mounting to the reed block that's an issue (XC reed block bolts are spaced 83mm, vs. around 60mm for a 38mm flange). I really don't want to swap out the entire intake block and reed assembly as you've apparently done.
Any help...from anyone...is always appreciated.

 

[firecrackerkid]

I didn't know at the time you could swap out the whole thing so I bought one of those $$$ adapters. I sold it along with most of the other pieces of the bike. Swapping for 430 parts probably a lot cheaper.

 

[2premo]

so do the 85-87 500 parts fit?
in 87 they used a 38mm on the 500

 

[gzrsbro]

I've done this before. Just made up an aluminum sleeve that fits over the smaller carb, with OD. of the stock carb. Then JB Welded it on. No hassle of changing intake manifolds. Worked like a charm.

Chris

 

[speedyauto]

Speedy,

Can you tell me the jetting you're using with the 38mm on your 500? I will be swapping out the 40mm eventually for a 38, but I don't imagine the jetting should stay the same as what I currently have in the 40. Just looking for a baseline, and I can go from there.

I'm really struggling with finding a suitable sized rubber intake flange to mount a 38 to the reed block of my XC500. No problem finding the right carb intake dimension (43mm diameter) but it's the bolt spacing for mounting to the reed block that's an issue (XC reed block bolts are spaced 83mm, vs. around 60mm for a 38mm flange). I really don't want to swap out the entire intake block and reed assembly as you've apparently done.
Any help...from anyone...is always appreciated.

Hey Geezer,
I'm currently running these specs in my carb
40 pilot jet
430 main jet
6DH3 needle middle clip
166 - R2 needle jet
3.0 slide
& I run 40:1 fuel ratio (500ml per 20ltrs) & it seems to be running fine.
As to the carb flange I'm using the stuff from my 430 so it does fit, there is also a machined alloy adapter that has a mikuni flange that can be bought thru 1 of the husky specialist on this site (cant remember which 1).
Good luck,
Speedy.

 

[Old Geezer]

Hey Geezer,
I'm currently running these specs in my carb
40 pilot jet
430 main jet
6DH3 needle middle clip
166 - R2 needle jet
3.0 slide
& I run 40:1 fuel ratio (500ml per 20ltrs) & it seems to be running fine.
As to the carb flange I'm using the stuff from my 430 so it does fit, there is also a machined alloy adapter that has a mikuni flange that can be bought thru 1 of the husky specialist on this site (cant remember which 1).
Good luck,
Speedy.

Thanks Speedy, I do appreciate all the detail. I WILL be switching to a 38mm someday but not until I get this MFSOB to light up as-is. All my searching, all the comments I've read, say that only about 0.005% of '83 XC500 owners can start their bikes. I was able to start it years ago with great difficulty when cold, then over time not at all. I haven't even got more than maybe 10 total run hours on it since I bought it damn near 8 years ago and I really really really want to ride it this spring! Been riding and messing with 2 strokes for over 40 years and so far this one is stumping me.

 

[speedyauto]

Thanks Speedy, I do appreciate all the detail. I WILL be switching to a 38mm someday but not until I get this MFSOB to light up as-is. All my searching, all the comments I've read, say that only about 0.005% of '83 XC500 owners can start their bikes. I was able to start it years ago with great difficulty when cold, then over time not at all. I haven't even got more than maybe 10 total run hours on it since I bought it damn near 8 years ago and I really really really want to ride it this spring! Been riding and messing with 2 strokes for over 40 years and so far this one is stumping me.

My first check would be that your ignition is working & diconnect the kill switch as they can be a pain & short out.
From my understanding the 50 pilot you said you are using will be causing you to sweat lots with no fire,
next make sure you have a really good earth, also make sure your plug is working & a .5mm gap (22thou I think).
So as I was told if there is spark, fuel & air it should run.
What I did 1st to get it running was make sure all the spark & timing (2.2mm before TDC but only ruff check)was right, fuel was not flooding the cylinder & nothing was blocking the jets or intake, then sweated my guts out trying to kick it but gave up & pushed started it. Magic when it fired & blew shit out the exhaust from somewhere & created smoke like a stream train but I got it settled down & found out my timing was 1.6mm BTDC & my pilot was to rich (it was unmarked but clearly bigger than a 40 pilot I had spare) since getting these things done it starts easily.
Dont be scared to push start it as it's easier than you think.

Cheers,
Speedy.

P.S. make sure there are no cracks in your intake boot, but the only other thing I can think of is that a crankcase seal is had it.

 

[Old Geezer]

My first check would be that your ignition is working & diconnect the kill switch as they can be a pain & short out.
From my understanding the 50 pilot you said you are using will be causing you to sweat lots with no fire,
next make sure you have a really good earth, also make sure your plug is working & a .5mm gap (22thou I think).
So as I was told if there is spark, fuel & air it should run.
What I did 1st to get it running was make sure all the spark & timing (2.2mm before TDC but only ruff check)was right, fuel was not flooding the cylinder & nothing was blocking the jets or intake, then sweated my guts out trying to kick it but gave up & pushed started it. Magic when it fired & blew shit out the exhaust from somewhere & created smoke like a stream train but I got it settled down & found out my timing was 1.6mm BTDC & my pilot was to rich (it was unmarked but clearly bigger than a 40 pilot I had spare) since getting these things done it starts easily.
Dont be scared to push start it as it's easier than you think.

Cheers,
Speedy.

P.S. make sure there are no cracks in your intake boot, but the only other thing I can think of is that a crankcase seal is had it.

Again, thanks for the input.

1. timing at 2.0mm, purposely retarded a bit to accommodate lower octane gas these days, ease starting, and to guard against kickback
2. New crank seal behind the stator
3. Carb boot in excellent shape
4. plug gapped at .020"
5. all grounds clean and shiny (stator, frame-to-motor, coil mount
6. spark when kicking (not the fattest spark I've seen but...). Will disconnect the kill switch just in case
7. pilot actually a 45 (thought I had a 50 in there, but checked again the other day and it's a 45)
8. float level set correctly
9. carb meticulously cleaned in and out
10. reeds seating properly
11. no obstructions in the exhaust (silencer)
12. lots of compression...using compression release installed in the head to help with kickover. I've never been successful with push starting down a hill (3rd gear, down my paved driveway, still just locks up the rear). Used to pull start it via a rope and another bike, and will be trying that again soon.
13. Swapped my bro's 40mm carb from his CR for fun....didn't start
14. With buckets of sweat and pulled leg muscles, I get a 'pop' out the exhaust once in a blue moon.

Possible that the wet-side crank seal is bad, though I never saw any indications (when it was running) of sucking in oil (no excessive smoke). Always a possibility, though, and one I don't even want to think about considering the work to replace it. Not sure I can split the cases without the proper tools.

 

[2premo]

so you have spark, you have commpresion, when you're done huffing and puffing pull the plug
is it wet or is it dry??

 

[Ron]

You don't need to split the cases to change either crank seals. The seals are held in a seal holder on the outer side of each center case. Accessible under the ignition on the left side and under the primary gear on the right.

 

[Old Geezer]

You don't need to split the cases to change either crank seals. The seals are held in a seal holder on the outer side of each center case. Accessible under the ignition on the left side and under the primary gear on the right.

That...sir...is good news! The stator side was a piece of cake, as will the primary side be. I'll replace that seal just to take it out of the equation.Thanks!

 

[Old Geezer]

so you have spark, you have commpresion, when you're done huffing and puffing pull the plug
is it wet or is it dry??

I did pull the plug and check after kicking, but it was the one time that my float stuck and overflowed...thus, the plug was wet as expected. Other times under normal circumstances it was dry.

 

[2premo]

I did pull the plug and check after kicking, but it was the one time that my float stuck and overflowed...thus, the plug was wet as expected. Other times under normal circumstances it was dry.

try to get fuel in there
if the carb is working correctly and this assumes the starting enricher
what is your air bleed screw set at, I call it air bleed becaus as you screw it out it adds air to a circuit that will be used to start your engine, if you are below 1000' try 1 turn out or less
if the plug is dry fuel is what you are missing

 

[firecrackerkid]

Thanks Speedy, I do appreciate all the detail. I WILL be switching to a 38mm someday but not until I get this MFSOB to light up as-is. All my searching, all the comments I've read, say that only about 0.005% of '83 XC500 owners can start their bikes. I was able to start it years ago with great difficulty when cold, then over time not at all. I haven't even got more than maybe 10 total run hours on it since I bought it damn near 8 years ago and I really really really want to ride it this spring! Been riding and messing with 2 strokes for over 40 years and so far this one is stumping me.

Here is your ignition running. Thought I had a vid of my brother starting it in his shoes but cant find it. i could not start it however.

View: http://www.youtube.com/watch?v=Ug_fiBZezQ0

 

[Old Geezer]

Here is your ignition running. Thought I had a vid of my brother starting it in his shoes but cant find it. i could not start it however.

View: http://www.youtube.com/watch?v=Ug_fiBZezQ0

Thanks big guy. I really never doubted the ignition. Even my internal rotor was sparking ok, but changed to your external for two reasons: get an even better spark at low kick rpms, and put the power band down a bit lower. When all this eventually comes together, and I do the 38mm swap, I hope to have a real stump puller!

 

[Old Geezer]

try to get fuel in there
if the carb is working correctly and this assumes the starting enricher
what is your air bleed screw set at, I call it air bleed becaus as you screw it out it adds air to a circuit that will be used to start your engine, if you are below 1000' try 1 turn out or less
if the plug is dry fuel is what you are missing

Air screw is at 1.5 turns, will try 1.0. Just last weekend when I did get this thing to at least fart a couple of times, it was with the old "blow through the floatbowl vent tube" trick...pressurizing the bowl and forcing fuel up through the needle jet to pool in the carb body. I may try this again, may even risk shooting some starting fluid into the air cleaner.

When I said 'dry' plug, by that I meant not soaking wet. At this point I 'assume' I'm getting fuel in there, unless my carb as well as my bro's carb are faulty (could be, his is a new project bike that we have yet to kick over...but the carb is clean as a whistle inside/out 'cause I cleaned it).

Will purchase a new plug today (gonna try a finer electrode B8EV) just in case and mess around again this weekend.

 

[2premo]

so the basics
when troubleshooting go one step at a time if you do everyting or even two things how do you know which one it was, I would start with the AIR bleed, go to starting fluid (which I don't reccomend) then checking the timing, which it sounds like you did, BUT MOST IMPORTANT ONE STEP AT A TIME
if you have spark I would look elsewhere, I could start my brothers CR500 in flip flops, the ignition made spark but not big, so it's the method not the extreme kick
people started their cars manually at one time so rpm is not the issue just easier

 

[Ron]

try to get fuel in there
if the carb is working correctly and this assumes the starting enricher
what is your air bleed screw set at, I call it air bleed becaus as you screw it out it adds air to a circuit that will be used to start your engine, if you are below 1000' try 1 turn out or less
if the plug is dry fuel is what you are missing

Not that any of this will help your starting issue:

The Mikuni choke is not really a choke but an enrichment system. A small carburetor inside the carb and should be used with the throttle closed. Opening the throttle allows the engine to suck additional air leaning the mixture and defeating the (choke) enrichener system.

In addition, kicking the engine slowly ?-times does not create a pressure drop in the carb, sufficiant to draw fuel up though the pilot jet.

Rocking in gear will cause fuel to slosh in the float bowl, in turn allowing fuel to slosh out from the pilot feed hole and spill into the motor.

I suspect the enrichment system does not supply enough fuel for cold starting these big bores.

My son is strong enough to kick his 390CR in rapid succession and it usually fires in 8 to 10 kicks.
I on the other hand, have never been able to start the 390, even when it's warm. Hence, I ride a 250 LOL.

 

[Old Geezer]

so the basics
when troubleshooting go one step at a time if you do everyting or even two things how do you know which one it was, I would start with the AIR bleed, go to starting fluid (which I don't reccomend) then checking the timing, which it sounds like you did, BUT MOST IMPORTANT ONE STEP AT A TIME
if you have spark I would look elsewhere, I could start my brothers CR500 in flip flops, the ignition made spark but not big, so it's the method not the extreme kick
people started their cars manually at one time so rpm is not the issue just easier

That's always been my modus operandi and I preach the same to those who work for me. I know the timing's good, I think the carb is good but will try adjusting the air screw. If that doesn't start it, then I know I can get gas into the motor by either sloshing or vent-blowing. I know I have spark and good grounds, but want to make sure it's as good as it can be...thus, a new plug.
I don't know if the primary seal is ok, so if I still can't get her to light then most likely I'll be throwing in a crank seal. And if it doesn't start after that, then I'll pull the jug and see if I have a stuck or broken ring or shot bore (though sure doesn't feel like it with the compression).

 

[steadydirt]

Again, thanks for the input.

1. timing at 2.0mm, purposely retarded a bit to accommodate lower octane gas these days, ease starting, and to guard against kickback
2. New crank seal behind the stator
3. Carb boot in excellent shape
4. plug gapped at .020"
5. all grounds clean and shiny (stator, frame-to-motor, coil mount
6. spark when kicking (not the fattest spark I've seen but...). Will disconnect the kill switch just in case
7. pilot actually a 45 (thought I had a 50 in there, but checked again the other day and it's a 45)
8. float level set correctly
9. carb meticulously cleaned in and out
10. reeds seating properly
11. no obstructions in the exhaust (silencer)
12. lots of compression...using compression release installed in the head to help with kickover. I've never been successful with push starting down a hill (3rd gear, down my paved driveway, still just locks up the rear). Used to pull start it via a rope and another bike, and will be trying that again soon.
13. Swapped my bro's 40mm carb from his CR for fun....didn't start
14. With buckets of sweat and pulled leg muscles, I get a 'pop' out the exhaust once in a blue moon.

Possible that the wet-side crank seal is bad, though I never saw any indications (when it was running) of sucking in oil (no excessive smoke). Always a possibility, though, and one I don't even want to think about considering the work to replace it. Not sure I can split the cases without the proper tools.

Suggest #15. [as it was not on the list]-hot new premium fuel