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Welcome to the club man......

My '85 Mille MHR starts fine, but only idles after a long, decent warm up, may take more than 10mls and/or minutes....
I learned to live with it..!!

Well now I have ridden the bike. Only did a short run around the neighborhood, about 5 miles. That's enough to put it through some turns and hit 70 MPH in places. What I found is the bike is running awful down low, under 3,000 RPM, but once above that it really takes off, pulls hard and sounds wonderful up to 7,000 RPM. The bike now has Conti replicas and K&N cone filters. I suspect the added air flow in and out is causing it to run too lean. Does anybody have any jetting recommendations? I'll find out what it's got now, I just assumed it was the stock set up but who knows.

If you don't want to destroy the engine, keep it under 3000 rpm's the first 6-7 miles.....
It takes up to 20 minutes driving, before any Beveltwin reaches operating temps....!!!!
I have an oil temp reader on my Mille, in summer it takes sometimes about 30 min. driving, before it reaches 80 degrees C.
The original handbook says: after start up in summer: let the engine idle for 5 minutes, before take of.
In winter, let it idle for 10 minutes before take of.....( I don't think my neighbors would like me to do that in winter, luckily for them, I don't drive it when temps drop...!)

Greetings from the land of the long white cloud.

I too am having an almost identical problem. I just can't get the bugger to idle, or respond to the mixture screws. To add to my woes the bike will change rpm, up and down, on its own while its idling. I'm guessing I've got an intake leak somewhere.

I was interested to hear your cure. I'll try a REALLY long warm up. It's driving me nuts. I've been 4 years restoring this thing and it looks fabulous. My wife says it's an ornament. Sad....

Let me know if it really was the solution, or you found a different answer please.

Regards

George

Hello George -

First I apologize for not posting the final outcome sooner. Second - I failed to learn from past experience with my Norton. I assumed that the carbs were jetted properly since the bike once ran and had 14K miles on it. I found out what the jetting was supposed to be, compared to mine and realized I had a mix of parts. Long story short, here's what I ended up using:

Main jet = 122
Pilot jet = 62
Slide = 50/3
needle = K6
Atomizer (needle holder) = 265AB

My needle and atomizer were way too small causing the bike to run very lean from idle to about 3,000 - 3,500 rpm. No amount of turning idle mixture or idle speed screws helped. The changes were a night and day difference. Now the bike idles fine ONCE IT IS WARMED UP. It still doesn't want to idle when cold. Throttle response is as it should be now without all the symptoms of running lean. You will want to be sure you have no vacuum leaks, as that will ruin everything when trying to get your carbs sorted.

My last step is to follow Steve's carb sync procedure and start riding, That is once the snow melts and the road salt is washed away. Right now that doesn't look like anytime soon.

Good luck and please let me know what happens. Thanks, Darrel

BevHevSteve wrote:Responding to a couple of previous posts:

On both the mixture screw and idle screw, take the spring and slide it over the screw then slide on the washer then the appropriate o ring. The purpose of the washer is to keep the spring from gouging the o ring.

Regarding left and right sides: yes there are left and right side CARB BODIES but there is no difference on the slides - they go in only 1 way only - there is no way to rotate around and install 180 off.

Yes if you have let the throttle slap closed and have worn out the idle adjuster ramp on the slide then you can take the slide out and put back into the opposite side carb - now that worn ramp does nothing as the adjuster screw rubs against the opposite ramp now.

Steve ... are you suggesting that BOTH the main idle (slide) screw and mixture screw should have springs, washers, and O-Rings? If so, my early-style PHM40's seem to be missing washers and O-Rings on the idle mixture screws. Washers and O-Rings are present on the main Idle (slide) screws, though. Can you confirm please?

Yes - that's why I said to make sure they were there. Can't tell you how many carbs I have rebuilt that were missing pieces.....

BevHevSteve wrote:Yes - that's why I said to make sure they were there. Can't tell you how many carbs I have rebuilt that were missing pieces.....

Well, that might explain why I couldn't get the bike to idle last summer. Looks like I'll be buying washers & o-rings for the PHM 40's idle mixture screws from the Bevel Store ... I assume you sell them?

I am very glad I stumbled upon this thread. I don't think I would have caught this.

After a full season (2016) without fuel in the carbs as I sorted out other "bugs" on the bike, the bike is now fully assembled again and ready for more shake-down testing.

I added 4 litres of fresh fuel to the empty tank and could see that fuel made it's way to the float bowls via the the hose.

After giving the throttle a few twists to get the accelerator pumps to squirt a bit into the carbs, I noticed the carbs are dry. In other words, no matter how much I twist the throttle, the accelerator pumps are not squirting any fuel into the throttle bodies. The fuel bowls are definitely full of fuel.

Needless to say, the bike isn't firing (yes, ignition is fine with lot's of spark from the fresh plugs).

Question: After sitting dry of fuel for a couple of years, could something have gone amiss with the accelerator pumps? Or, do I need to add more fuel into the tank to provide more pressure since 4 litres puts the tank on "reserve".

Thoughts?

Thanks,
Herb...

Hi Herb, you only need to prime the pumps.

Remove the non return valve, put a teaspoon or so of gas into the hole, put your thumb over the hole and pull the cable a few times until gas squirts out the pump jet.

You may have to pull the cable several times, you may also need to put more gas into the pump housing.

Repeat same steps on other carb.

Thanks Steve.

Sorry if I sound like an amateur but if I remove the non-return valve by removing the float bowls, how can I get a teaspoon of fuel in the hole with the carbs connected?

Am I missing something in your explanation?

Thanks,
Herb...

The other non return valve.... it's on the top of the pump housing.

Item # 54 in the attached drawing.

Thanks for clarifying and including the drawing. Nevertheless, I was successful in getting the front Accelerator Pump to squirt a bit of fuel in the body
when I held my finger over the hole (after removing the non-return valve). I didn't need to add gas in the hole.

So, got the bike running and warmed up. All is good until I let it cool, and noticed that the accelerator pumps weren't squirting gas into the body again.

Removed the non-return valve and tried the finger over the hole routine again but this time, no squirting gas. Next, I took the accelerator pump housing off the front carb and carefully pulled the throttle to inspect the diaphragm valve. The diaphragm appeared to be ok and looked like it was working - sticking out a bit as the slide ramp went up the cam. Blew out the housing and re-assembled and still no squirt.

Now, I'm thinking something is intermittently defective in the carbs. Could it be the diaphragm? I tried to remove the pump jet for inspection but after unscrewing the pump jet holder, I did not want to apply force on the pump jet as it seemed difficult to remove.

Anyway, it appears that my starting issues are completely connected to not getting squirts of fuel into the carb bodies. Something is stopping from the accelerator pumps from working reliably.

Suggestions on next steps?

Thanks,
Herb...