jetting advice

[bronco70]

looking for advice i went thru this already and welcome the good advice yawl give
running rich and fouling plugs i thought i had it close but its still fouling plugs
carb is 26mm on 125cc combat 95 already change pilot jet from 45 down to 40
main jet is now 180 bike seems to run good thur all ranges but after 7 or 8 rides
of 1/2 hour or less it fouls plug when you go to restart
i am thinking about changing pilot jet down to 35 since right now
on the 40 i am at 2 1/2 turns out. does this sound like my best next move??
or should i go from b8 plug down to b7 ?

now running 93 gas with 28 to 1 mix amsoil
b8 plug

[Bullfrog]

Here are the factory specs for the original 28mm spigot mount carb on the piston-port Combat Wombat engine.
Pilot Jet - 25
Pilot Air Screw - 1.5 turns out
Throttle slide cut-away -2.5
Needle Jet - O4
Needle - 5EJ13 - clip in third notch
Main Jet - 190

IF (repeat IF) you still have the original carb AND the engine, air cleaner and pipe have not been modified (any more than your racing silencer project) then the above specs should be quite close for you. HOWEVER, if you have a different carb, modified air cleaner or modified engine porting . . . then all bets are off.

I would recommend sticking with the "8" heat range plug. That is what I run both on the trail and on the track in my piston-port Combat Wombat engine without fouling problems. The original factory spec called for a "9" heat range plug . . . but that was just plain too "cold" (and we knew that in the 70's).
Ed

[Hydraulic Jack]

Generally, changing heat range on the plug is not a cure for fouling. 28:1 is probably more Amsoil than you really need for trail riding, but change only one thing at a time or you will just get lost. Especially if you do a lot of idling, running slow or at low rpm, your fuel mix will tend to accumulate in the crankcase (perhaps you have heard the term "loading up.")

Something you might try when coming in from a ride, when you get home and are ready to park, shut off the gas but let it run at modest rpm just off idle until it runs out of gas. Your problem could be nothing more than a misadjusted float level that lets gas dribble down the intake when parked with the bike tilted on the kickstand. Emptying the float bowl will help keep the crankcase dry if you have a small leak in the petcock or float needle, so that the next time you start, you start fresh. If you have not been fouling plugs while riding, but only on cold start after it has sat for a while, it may well not be the jetting.

[Bullfrog]

. . . and unless you are racing or doing a lot of road riding (or ANYTHING) involving long periods of high rpm running I see no reason to run more oil than 32:1 or 40:1. I ran 40:1 in the 1970's in one-hundred-fifty to two-hundred mile per day ISDT Qualifier events. Since most of my riding on my Combat Wombat these days is on the track, I run 32:1 premium auto gas (non-ethanol) and Yamalube R.
Ed

[bronco70]

i wish it were left stock when i got bike reeds had already been added and victory ports drilled in clyinder
so i have 26mm carb not the 28 that should be there it had 45 pilot jet and 130 main when i got it
but it was not running and dont know what mix he was using so i orederd a bunch of jets and started
main at 220 and worked down to 180 this work good for wot but still seemed rich so i changed pilot to 40
and still had to drop needle down to last notch to get it to run clear at mid to 3/4
bike seems to run good now but keeps fouling plugs so i assume with the 40 pilot jet at 2 1/2 turns i need
to drop down at least 1 more step to 35 ? i may go ahead and buy a 30 also just in case


thanks for the input guys your help is priceless

[Bullfrog]

OK - reeded Combat Wombat with 26mm carb. Just ignore the previously posted CW specs - they simply don't apply to your situation.

I would expect (but recognize that this is a SWAG - Scientific Wild A_ _ Guess) that a main jet in somewhere near the 200 region would be right . . . and that a pilot jet near the 40-50 area would dial in with the pilot air screw near 1.5 turns out. Reeded engines always REQUIRE richer jetting than they did with the same carb prior to being reeded. (Wombat 03 engine uses a 26mm carb and has a 50 pilot jet and 180 main jet standard.)

NOTE: Reeds which are not sealing to the cage (warped, damaged/frayed, wrong size) will cause "richness" even when the proper jetting is installed in the carb. So check the reeds.

NOTE: "Dial in" the proper pilot jet 1st. Then go after other components.
Ed

[bronco70]

i will check reeds again danny cooke looked at them and thought they were ok when i 1st got bike
what you said about pilot jet being around 40-50 is where i get lost since i started with 45 pilot and it would run ok at 1 1/2 turns out
and had dialed in on 190 main still seemed rich went down to 180 main bike ran good wot but seemed rich at idle to 1/2 and was fouling plugs
so i change pilot to 40 and thats where im at now with 2 1/2 turns out with new baffle , so this is my trouble seems if i go back up in pilot jet
riches would get worse or am i missing somthing about pilot jets? i was think since with 40 jet at 2 1/2 turns out this is pointing to going smaller
so i was going to oreder a 35 and 30 just thinking that since 40 is at 2 1/2 that 35 would be closer to 1 or 1 1/2 ?? please help me get un confused
if i am thinking wrong

thansk again guys

[Bullfrog]

Bronco70,

I recommend that you do a bit of a review on the procedures for tuning a Mikuni. One of the first things you will learn is that when you are searching for the correct pilot jet - the way you know that you have the correct one is that things will be "right" when it "tunes in" with the pilot air screw at 1.5 turns out.

It doesn't make sense that " . . . I started with 45 pilot and would run OK at 1.5 turns out . . ." and then ". . . so I change pilot to 40 and that's where I am now with 2.5 turns out . . ." The 45 was OK, then you went to a leaner pilot jet AND adjusted a full turn leaner on the pilot air screw? Something is not right there.

So, try this:
- Note your pilot jet size and set the pilot air screw at 1.5 turns out.
- Start engine and let it warm up. Set the idle speed where you would like it using the idle adjuster screw.
- Turn the pilot air screw out 1/4 turn and wait to see what happens to idle speed. Did it speed up or slow down? If it sped up, turn the pilot air screw out another 1/4 turn and wait to see what happens. If, on the other hand, it slowed down, slowly turn the pilot air screw IN to the 1.0 turns out point and wait to see what happens. If it speeds up by turning IN, then turn IN another 1/4 turn and wait to see what happens.
- By repeating the above process with various pilot jets, and searching for the maximum idle speed adjustment which results from various pilot air screw settings . . . you will ultimately find a pilot jet which is just right with the pilot air screw 1.5 turns out (acceptable range is 1.0 to 2.0 turns out, with a target of 1.5)

You should complete this pilot jet/pilot air screw tuning procedure BEFORE messing about main jets (which is OK because you never have to leave the garage to find the right pilot jet).
Ed

[Bill2001]

Google "mikuni tuning manual" and you can download a jetting manual. And jetting techniques are described in the Hodaka shop manuals.
Remember that the idle mixture screw is an idle air screw-- turning it in richens the mixture and turning it out leans the mixture.
And the jetting components affect different parts of the throttle range. The pilot jet works in the idle-1/4 throttle range ( tho it contributes over the entire range). The needle/ needle jet works in the range from 1/4 to 3/4 throttle. The main jet works in the range of 3/4 to 4/4 (full) throttle, as well as contributes over the entire range.
In a nutshell, put simply.

[bronco70]

Bronco70,

I recommend that you do a bit of a review on the procedures for tuning a Mikuni. One of the first things you will learn is that when you are searching for the correct pilot jet - the way you know that you have the correct one is that things will be "right" when it "tunes in" with the pilot air screw at 1.5 turns out.

It doesn't make sense that " . . . I started with 45 pilot and would run OK at 1.5 turns out . . ." and then ". . . so I change pilot to 40 and that's where I am now with 2.5 turns out . . ." The 45 was OK, then you went to a leaner pilot jet AND adjusted a full turn leaner on the pilot air screw? Something is not right there.

So, try this:
- Note your pilot jet size and set the pilot air screw at 1.5 turns out.
- Start engine and let it warm up. Set the idle speed where you would like it using the idle adjuster screw.
- Turn the pilot air screw out 1/4 turn and wait to see what happens to idle speed. Did it speed up or slow down? If it sped up, turn the pilot air screw out another 1/4 turn and wait to see what happens. If, on the other hand, it slowed down, slowly turn the pilot air screw IN to the 1.0 turns out point and wait to see what happens. If it speeds up by turning IN, then turn IN another 1/4 turn and wait to see what happens.
- By repeating the above process with various pilot jets, and searching for the maximum idle speed adjustment which results from various pilot air screw settings . . . you will ultimately find a pilot jet which is just right with the pilot air screw 1.5 turns out (acceptable range is 1.0 to 2.0 turns out, with a target of 1.5)

You should complete this pilot jet/pilot air screw tuning procedure BEFORE messing about main jets (which is OK because you never have to leave the garage to find the right pilot jet).
Ed

just to clear up the waters i seem to have muddy up
i had 45 pilot jet at 1 1/2 before i messed with my pipe and added baffle it was still fouling plugs so it was still rich but after i did pipe and baffle
i had to run 45 pilot out around 3 turns to get it to idle thats why i swaped it for 40 pilot which is at 2 1/2 turns out any thing further in and it wants to die i will try your method since i was starting 3 turns out and going in untill motor started dieing you way seems best
thanks again for the help

[Bullfrog]

Bronco,
Good to hear. My comfort level is going up with your more complete report of the history . . . and with the adjustment to your tuning processes.

Since you want end up at 1.5 turns out on the pilot air screw, starting there allows you to work both ways from the target to find out which way is better for the engine. AND the direction you have to go (IN or OUT), gives you an indication of whether you need a bigger or smaller pilot jet. Right now, you have a 40 and you had to go OUT to get it to run right - so a test with a 35 seems in order.

Finally, lets not put too much weight on "fouling plugs" as an indicator of "richness". Richness/leaness is identified by ear and smooth throttle response . . . not so much by plug fouling (though it is an indicator). Plug fouling can be caused by host of other things too - and there is a DPO involved here (Dreaded Previous Owner) so who knows what else you may find. Example: a "weak" ignition (pitted points, bad solder joint on the condenser, failing condenser, crusty connectors, etc.) could really complicate things by being the root cause of the plug fouling AND making it almost impossible to do proper carb jetting. (Can't do proper jetting if the ignition system isn't up to snuff.)
Ed
PS: Are you having fun yet?

[bronco70]

thanks ED you bring up some good points.i went ahead and ordered pilot jets 35,30,25 one of these has got to be in right range
i dont think i have ever had this much issue getting bike jetted before. but with all the mixed up parts that dpo (in my case dead prevoius owner)
slapped on this bike it sure makes it pain in the butt to get right. it is starting to take some of the fun out of it.but i am not giving up
and glad to have this fourm to get advice

thanks again

[Bill2001]

And remembered because a jet is marked "100" it may have been drilled. Look closely at the needle for wear. Plan to replace the needle jet. Evaluate the slide cutout for reshaping. And so on. A DPO can be tricky.

[Hydraulic Jack]

it is starting to take some of the fun out of it......

Now you know why there have always been more owners than mechanics. Work is work. Diagnostics isn't as easy as it seems. The Mikini is one of the easiest carbs to tune, but as mentioned, there are a host of other things that can so interfere with the process that jetting alone won't solve problems.

Start your approach by assuming nothing. After all, the bike was made in a different century. Verifying the ignition may not sound like a jetting procedure, and maybe it isn't, but getting an old bike to run like a new one requires everything critical to proper function to be working 100%. Timing, compression, absence of air leaks in the intake tract, absence of leaks in the crankcase, base gasket and head gasket, all ignition system wires sound and not broken inside the insulation, ignition coils with proper resistance, condenser with proper impedance....all need to be verified. If these things are assumed rather than verified, you could be at the jetting thing for a long time.

[rlkarren]

Sharing for reference:

I have a 94 Wombat with a CW top end, ported with Reed intake. Stock CW 28mm carb, but the pilot is a 35 and the main is currently 240 @ 4500 ft elevation. 24:1 fuel mix. Also using a 94 Wombat pipe, (for now), with the baffles cut off the spark arrestor and replaced with open pipe, (similar to what Danny Cooke did to his).

I haven't gotten it dialed in completely but I am confident that I am very close now. The plug is still a little more pale than I'd like to see it.

Roger

[MTrat]

And remember the old 'Known Good' method of solving tuning enigmas. If possible, isolate your problem by substituting a questionable part or system with one that you know works. If the ignition doesn't ignite or the carburetor doesn't carb, try another if available. This may not apply to pistons---

[bronco70]

while i am waiting on the mail man to bring my new selections of pilot jets i did as ed recomended
with the 40 pilot jet, i started at 1 1/2 turns out and if i turn it inward motor slows down if i turn it out
past 1 1/2 turns there is no real noticable change untill i hit 3 1/4 turns then you can hear differnt exuaghst
note and idle speeds up slightly ,if i keep going more 1/4 more turn seems to lose that differnt sound .so i think
based on that going to 35 pilot is justified . i will do same test with 35 if it hits sweet spot around 1 1/2- 2 turns
i will move to testing main jet again. if not i now have pilot jets ordered from 45 down to 25 so i should be able to
find right one.points look good and fire is strong bike will start 1st kick every time unless plug is fouled

[matt glascock]

Since you are heavily inflicted with the DPO syndrome, is there and possibility you are trying to tune with an incorrect air screw? That would really make things fun.

[bronco70]

Since you are heavily inflicted with the DPO syndrome, is there and possibility you are trying to tune with an incorrect air screw? That would really make things fun.

I dont think he swaped air screw but I guess I cant
Be sure .it appears that he used reeds intake and carb off 03 wombat or road toad

[matt glascock]

Unlikely though it would be, one never knows what nifty innovations may be lurking in the wake of the DPO. Maybe he was a mad tuning genius that specified an air screw exchange for the perfect power band.

[bronco70]

ok after getting muffler/baffle with sound i wanted here is where i am on jets
pilot 40 with screw 1 3/4 turns out
main jet 190
needle on 2nd notch from top
bike runs real well just a little rich sputter about 1/2- 3/4 throtle 2nd gear only clears right up unless you hold throttle in that place
strange thing it does not do it in any other gear.here is pic of plug could i get some of the experts opions?

thanks again guys

[taber hodaka]

2nd gear only clears right up unless you hold throttle in that place?? Not sure of your statement and what plug?--Clarence

[bronco70]

2nd gear only clears right up unless you hold throttle in that place?? Not sure of your statement and what plug?--Clarence

motors seems to have a little rich sputter (4 clycling ) just a little past half throttle and if you hold that throttle postion it want clear up
but if you give more or less throttle it clears up . but it does not do the same in any other gear .
the plug is b8 hs posted picture to see comments how it look to others i think it looks like running rich

[taber hodaka]

Just my thoughts, if your bike is running lean don't try tuning or jetting by reading the spark plug. You could stick the engine before you got started. To me the plug reading is a overall indicator. There can be a big difference between fun riding and racing,types of oil, spark plugs and mixing ratios. If your plug looks on the rich side and it doesn't foul that is good. Let me try to explain it this way, as your throttle is held at 1/4, in second gear on a uphill grade. If the sound is blubber blubber blubber you are too too rich. If it is EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE you are too lean. to me it should sound eeeeeeeeeeeeblipeeeeeeeeeeeeeeeblip,blipeeeeeeeeeeeeeeeeeeblipeeeeeeeeeeeeeeeeeeeeeblipeeeeeeeeeblip. And I would repeat for all the gears. And if you are not mechanical I would have a tuner tune it. It may not be rocket science but it is science. If you are too lean at half throttle do not check full throttle. I would start with stock settings but a larger main jet. Dial in from the rich side. I would run the coldest plug it will run with without fouling. cooler run engines produce more power only my opinion. -----Clarence

[Bullfrog]

Your comment about it not doing the same blubber at 1/2 throttle in any gear except 2nd probably comes from the fact that the engine is not really "pulling" at steady 1/2 throttle in 2nd (and you just won't leave it at half throttle in 1st - note that I wouldn't either). Anyway, jetting is supposed to be checked with the engine "loaded" (made to work, not just "wind-mill"). So I think it is a good sign that it doesn't blubber in the higher gears - ASSUMING that you "found" the carb setting which DID blubber in the higher gears, then went ONE step leaner to arrive where you are now.

I kind of like the look of the plug. It MIGHT be showing slightly rich, which is what I sure as heck would want on a bike I'm just getting used to. But PLEASE don't do your jetting based on plug observations, OK? Take some time. Ride the machine. Carry a couple of spare plugs. If you find your jetting is indeed on the rich side and it is causing you problems with rideability or spark plug life . . . figure out what throttle position is rich and tweak that. Make ONLY one adjustment at a time, so you can gauge the effect of that ONE change - BEFORE making any other change.

By the way, what brand and heat range of plug is shown in the most recent photo?

How does a 200 main jet run at full throttle?

Ed