Strange Occurence

Hello,
My amal 932's did some weird activity during last nights ride.
I usually putter around so wide open throttle blasts are rare.
In 4th gear wide open throttle it gasped like someone knocked the wind out of her.
Seemed like no fuel at full throttle.
Carbs recently resleeved at Lunds. Idles perfect. 1 start kick.
Throttles up nicely to 6 grand 1st through 3rd gear.
Shift into 4th and crack the throttle WO and it is like one big dead spot.
Back off the throttle and it recovers at about 3/4-1/2 open range .
Carb internals are all uk amal parts. 106 needlejet. Clip in middle combat
position on needle. Stock main jet.
Before I start re-ripping a nice recently rebuilt set of carbs apart like a rookie
what if any leads should I persue? I don't want to just take things apart to takes things apart.
Thanks in advance its 1:42 am, I hope I made sense.
Marshal

Hi

What's the type of air cleaner and the size of the main jets ?

Cash

I recently had an occurance similar to that, I wound the bike up to 6k and it cut out like it was starved for fuel. I coasted and let the RPMs drop and it started running normally. I thought to myself that I would have to follow up on it and get into the carbs when the weekend rolled around. I kept riding the bike and over he next few days I had reoccurances at lower RPMs. I did two things. I checked the connections at the battery and the fuse holder, and I cleaned the kill switch with electromotive cleaner. The problem is gone (for now). Worth checking before you get into your carbs.

Russ

Cash,
stock ham can air cleaner with K&N filter just recently cleaned and relubed.
main jet isstock specs for 72 combat. I don't want to guess so I have to say I forget what's in there.
Russ,
I'll check electrics. Seems weird it is ok except at wide open in top gear?
Marshal

I had the same thing happen a few times, not sure if it was the reason but I found the top of my Mikuni to be loose & almost coming off. Have not had a chance to see if it's still doing it or not.

Marshal, It is certainly a "symptom" of Leanness up high, usually more detectable in Top gear as you are there longer than in the lower gears.
What's happening is the engine is gasping for more fuel, bigger main needed, or possibly floats lowered to allow more fuel in when needed, (prolonged sucking) and when you roll off the throttle ( close the slide ), It regains it's state of tune at 3/4 throttle. It should do it in the lower gears as well, but if you'r not used to revving your engine hard, you may not have notticed it.
Freshly oiled K&N's can richen things up, but only momentarily, then reveal a situation like this.
The top coming loose on gtsun's Mikuni would certainly lean things off.
Having said that, It is most definately worth the effort to search through the electrics first as symptoms can be simmilar.
AC.

If you have a choke lever fitted, try giving it some choke before the WOT.

If you have chokes fitted, make sure they are both up out of the way in normal running.

You also sometimes hear of a needle dropping down too, although you'd expect the other cylinder to try harder.

Check your jetting - wrong main jets or wrong needle jets could do this too.

And that the fuel taps can flow enough fuel out of the tank.

Opethiselps.

Oh! & don't forget the obvious easiest, is your petrol cap letting air in.

I went to a company sponsored problem troubleshooting course at one of my old jobs years ago and the first question would be "What has changed?"

Recently cleaned and relubed K&N air cleaner? It can take a while for the excess filter oil to dissipate by dripping off, getting sucked in etc. Ride it some more and see if it improves. Ride it up here and we'll go for a spirited blast in the woods around Haycock Mountain.

Russ

Depending on the color of the plug, raise or lower the needle 1 clip groove. If dark lower the needle, if light raise the needle.
This is not only the most logical place to adjust, it is also the easiest. Oop,I ibetter say "IMHO" cause someone will surely disagree.

I might thing that because is it all rebuilt and tightened up, that any air that was getting in has now been sealed. A rich condition might be assumed. The plugs should tell.

I had similar symptoms years ago after overfilling the oil tank. Oil from the breather saturated the air filter. Bike ran OK until it was under load.. going up hills, 4th gear WOT, etc.

More recently I had a problem maintaining speed on the highway - it turned out to be the little plastic fuel filter I was using just couldn't supply enough fuel to keep the bowls full. At 60 mph it was OK, but at 70 it ran out of gas.

MarshalNorton said:

Russ,
I'll check electrics. Seems weird it is ok except at wide open in top gear?
Marshal

Click to expand...

I really thought I was starved for fuel, I was wound out to 6k in 3rd gear climbing a hill. I even pulled my banjos off and checked the fuel flow and the screens (forgot to mention it in first post). The problem started showing up at different RPM levels and without any particular pattern over a period of days. I don't have a clue why it would behave that way exactly. I just know that it quit when I checked and cleaned the electrical connections and the kill switch.

I just took the switch cluster off my handle bars and sprayed it with electromotive cleaner while pushing the kill switch to open it. I checked it with a good quality ohm meter to make sure it was getting good contact. Sadly when I first checked the resistance before cleaning I was on the wrong posts in the switch (which of course gave a high reading through a light bulb!) so I don't have a comparision. I should have gotten my reading glasses out before getting started instead of after!

Russ

Seems like fuel and that's last area handled so directly implies electrical especially when pattern varies, so like knocked some thing lose dealing with filter. Some times a fuse or its mount can do this. Ok unless engine vibes messing with it so harder to diagnosis. Always worth while to look at it in the dark.

Re: Strange Occurence Solved

Solved It!!!!!!!!
I removed the timing side float bowl drain plug and behold there nestled inside it was my 230 main jet.
Screwed it up nice and tight with a thin walled 8mm socket and checked the other side for safe measures.
Road test results:
It ripps now :mrgreen:
If only all things were this simple.
i thought to check for something dropping as one poster recommended.
Thnaks
Marshal