What main jet size are you using in your Combat?

ILLF8ED · Feb 18, 2010

Hi Combat owners,

What main jet size are you using in your Amal 932s? 230 was original, I went to 240 and now trying 260 to see if the pinging will go away. Noticed full advance at 15 degrees BTDC does work to eliminate pinging, but the engine doesn't like to start.

Also what fuel are you using? Benchmarking to see where to go next.

Thanks,

bill · Feb 18, 2010

I am at 190 mains. stock air box, 28 deg timing, rita ignition and viking exhaust. mine does not like larger mains or regular fuel but it is OK on premium. I also cut .020 off the tops of the pistons when I built the motor.

grandpaul · Feb 18, 2010

Exxon is the worst gasoline you can buy, period. Thier highest octane is absolute donkey pee (no disrespect meant to any donkeys or donkey lovers)

I like Valero best, then Chevron, both mid-grade product.

swooshdave · Feb 18, 2010

grandpaul said:
Exxon is the worst gasoline you can buy, period. Thier highest octane is absolute donkey pee (no disrespect meant to any donkeys or donkey lovers)

I like Valero best, then Chevron, both mid-grade product.

I think what he meant was octane. Are those both 89?

ILLF8ED · Feb 18, 2010

What I'm looking for is what main jet size the combats are using. So far 190. I'm at 260 now, but thought the engine ran better with 240. Even with 260 mains the engine will pull to 7,000 redline rather quickly. Still playing with it.

I have a RITA ignition set at 28BTDC full advance unless the timing marks on the new Wassel rotor are whacky - could be, standard 10:1 compresion setup (may closer to 9.5:1). Cylinder compression 183psi left 185psi right. Using Arco or Chevron 91 octane gas. Will get some race gas this week to try blending to see what happens. Carbs are original 932s with Gaylord sleeving.

debby · Feb 18, 2010

Have you calibrated the timing scale in your chaincase? They can be way off. Your timing may not be what you think it is.

FWIW, in my 850 I'm running 220 main jets here at 5000 ft. elevation. 260's were stock. In my non-Combat 750 with 930's I'm running 180 mains and they're a little rich above 10,000 ft. Down here on the prairie they're good. No pinging in either bike. I checked my timing marks on both bikes with a degree wheel and they were only off a couple of degrees. I've heard of some bikes being off as much as 10 to 15 degrees though.

Debby

ILLF8ED · Feb 18, 2010

debby said:
Have you calibrated the timing scale in your chaincase? They can be way off. Your timing may not be what you think it is.

FWIW, in my 850 I'm running 220 main jets here at 5000 ft. elevation. 260's were stock. In my non-Combat 750 with 930's I'm running 180 mains and they're a little rich above 10,000 ft. Down here on the prairie they're good. No pinging in either bike. I checked my timing marks on both bikes with a degree wheel and they were only off a couple of degrees. I've heard of some bikes being off as much as 10 to 15 degrees though.

Debby

Hi Debbie,

You're probably saying the same thing, but my uncertainty isn't the degree scale, rather the new Wassel rotor's timing mark may not be in the correct location. Will have to compare it to the previous original rotor

Stock combat mains are 230 at sea level.

bpatton · Feb 18, 2010

David,
How long has it been pinging? Was it fine before the new rotor? I checked the timing marks on my bike a few years ago and they were about 8 degrees off. Don't know if it was the rotor or the markings on the scale. Just out of curiosity, what cam are you running and when is the pinging happening? Lower revs under load? WOT, on the mains? I skimmed a head once on my 850 to get 10:1 and got some serious pinging, the engine was otherwise stock. I was told that I was asking for it running that high a CR with the mild cam. I changed it for some thing hotter and the pinging went away at low revs. Has to do with the overlap or something. They do sing when they come on the cam. BTW, this was when gas was of a generally higher quality.

kraakevik · Feb 18, 2010

Last summer I dropped the main jets from 230's to 220's on my Combat (.020" over 10-to-1 pistons, balanced exhaust, Dunstall mufflers, 106 jets with needles lowered all the way). I've been pretty pleased with the results and will be experimenting with 210's and 200's when things warm up. The engine likes premium and wlll lose a little punch and mileage even with midgrade--it's a false economy for a dime or two per gallon.

Tim Kraakevik
kraakevik@voyager.net
'72 Combat

MarshalNorton · Feb 19, 2010

My '72 combat is like it left Merry Ole England, bone stock.
I left the timing at the orig. 28 degree mark. I have no pinging issues.
I run Sunoco 93 premium if filling out on a ride.
If I have to add fuel from home, I keep a can of 93 octane Sunoco w/ an octane booster which I'll fill it up w/.
I like to throw a couple ounces of Marvel Mystery oil in a 2.5 gal can and shaken not stirred.
It kinda fogs the cylinder as you ride and keeps everything nice and protected.
Yeah, it is a pain in the ... to mix every time if you ride allot but for periodic riding it is peace of mind.
My commando goes like hell stock w/ this receipe.
Again I'm stock w/ 9600 miles on her.
Maybe she just hasn't worn out yet?
Marshal

ILLF8ED · Feb 19, 2010

bpatton said:
David,
How long has it been pinging? Was it fine before the new rotor? I checked the timing marks on my bike a few years ago and they were about 8 degrees off. Don't know if it was the rotor or the markings on the scale. Just out of curiosity, what cam are you running and when is the pinging happening? Lower revs under load? WOT, on the mains? I skimmed a head once on my 850 to get 10:1 and got some serious pinging, the engine was otherwise stock. I was told that I was asking for it running that high a CR with the mild cam. I changed it for some thing hotter and the pinging went away at low revs. Has to do with the overlap or something. They do sing when they come on the cam. BTW, this was when gas was of a generally higher quality.

Hi Bob

It's been pinging off and on for the last couple of years. Got worse at the end of last season. Original combat cam and combat spec on the engine. Mechanically it's in excellent condition. Just checked the timing mark/scale with a timing wheel on the cam. It matches perfectly. I'm going for race gas next and start blending with 91 octane unleaded/ethanol until I find a good mix. I'd rather go to the trouble with special fuel than give up the combat performance. Good thing I don't rely on it for transportation.

I see some going to small mains, however the cure for pinging is going larger to richen the mixture, cooler flame. If I'm wrong someone sign in.

Thanks,

Danno · Feb 20, 2010

illf8ed said:
bpatton said:

David,
How long has it been pinging? Was it fine before the new rotor? I checked the timing marks on my bike a few years ago and they were about 8 degrees off. Don't know if it was the rotor or the markings on the scale. Just out of curiosity, what cam are you running and when is the pinging happening? Lower revs under load? WOT, on the mains? I skimmed a head once on my 850 to get 10:1 and got some serious pinging, the engine was otherwise stock. I was told that I was asking for it running that high a CR with the mild cam. I changed it for some thing hotter and the pinging went away at low revs. Has to do with the overlap or something. They do sing when they come on the cam. BTW, this was when gas was of a generally higher quality.

Click to expand...

Hi Bob

It's been pinging off and on for the last couple of years. Got worse at the end of last season. Original combat cam and combat spec on the engine. Mechanically it's in excellent condition. Just checked the timing mark/scale with a timing wheel on the cam. It matches perfectly. I'm going for race gas next and start blending with 91 octane unleaded/ethanol until I find a good mix. I'd rather go to the trouble with special fuel than give up the combat performance. Good thing I don't rely on it for transportation.

I see some going to small mains, however the cure for pinging is going larger to richen the mixture, cooler flame. If I'm wrong someone sign in.

Thanks,

No, you are right, not so much for a cooler flame, but a slower one. You may have some success with octane booster like 104+ or similar. The high-comp motor detonates the charge before the spark and causes pinging. Higher octane burns slower so it can't light early. Richening may not do the trick, though.

MarshalNorton · Feb 20, 2010

I've been riding my Norton Combat since May 2008.
I purchased it July 2004 and have read all the possible ways to "improve" it.
It seems allot of mods end up coming full circle back to a stock configuration.
ie... the whole breather forum for example. Some have realized the relocation was in vain.
I would leave your combat stock for the purpose of fuel delivery. The more you play the further away
you get from solving the issue.
Get some CAM 2 fuel at $6.00 a gallon. Agh... fill it up it's only 2.5 gallons.
Then let me know how that "pings".
Our bikes were designed before the Govt took the fun outta fuels. 8)
Marshal

rvich · Feb 20, 2010

I would be curious if anybody has tried an S4 cam in a Combat?

ILLF8ED · Feb 20, 2010

I think my question has been answered. Going larger on the main jet didn't solve my pinging. The timing mark is accurate and even at 26 BTDC full advace with a RITA ignition, 260 mains, 91 octane, the problem persists. Race gas seems to be the last solution. Several have commented on this forum about Marvell Mystery oil. Is this just a lubricant like adding oil to a 2 stroke or does it reduce detonation?

What main jet size are you using in your Combat?

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