Bike dies at stops

swooshdave · May 25, 2020

In the past I would have problems with the bike dying after a hard ride and I'd come to a stop. I assumed it was something electrical getting too hot.

Now I'm having a different issues, I'll ride and come to a stop and the bike just won't idle. The revs just drop. I can adjust the idle screw back up (I have one of Don Pender's single cable set ups) and it will start and idle just fine. Next stop same thing. Rinse and repeat.

Statically it will just sit there at whatever idle I want. But as soon as I go for a ride it dies at the stops. The idle screw is very hard to turn so I can't imagine it turning by itself but that's one possibility.

Thoughts?

Otherwise it's doing fine considering I've only put a few miles on it since the rebuild. Also I had forgotten just how long of a stretch it is to the clip ons. And how much you have to look up to see anything. I need to get the neck a lot more limber.

rvich · May 25, 2020

I'd be checking the pilot jet circuit and making sure it doesn't have an air leak where it is plugged in the intake opening of the carb.

cliffa · May 25, 2020

Dave, why not mark the idle adjuster with a permanent marker and see if it's moving?

cliffa · May 25, 2020

The bike looks great by the way !!

rvich · May 25, 2020

In this photo, I'm talking about where it is labeled "gas side is plugged". An air leak there drove me crazy trying to keep my idle set until I discovered it and plugged the leak I was experiencing the same situation.

Tornado · May 25, 2020

rvich said:
View attachment 16472

In this photo, I'm talking about where it is labeled "gas side is plugged". An air leak there drove me crazy trying to keep my idle set until I discovered it and plugged the leak I was experiencing the same situation.

Never assumed that plug was a potential leak. Good tip to check. What did you use for sealing?

swooshdave · May 25, 2020

cliffa said:
Dave, why not mark the idle adjuster with a permanent marker and see if it's moving?

That was next on my list.

Thanks for the replies, the puzzling part is I can get it to idle just fine so that it why I didn't suspect the idle circuit.

rvich · May 25, 2020

Tornado said:
Never assumed that plug was a potential leak. Good tip to check. What did you use for sealing?

It has a tiny bit of JB Weld smeared over it now. Initially I just put a dob of RTV gasket maker on it.

I think I was adjusting to counter for the air leak when static but when dropping from a higher RPM the pilot circuit did not adjust to the change correctly as it was sucking from both the bowl and the plug area. It's a theory.

cliffa · May 25, 2020

swooshdave said:
That was next on my list.

Thanks for the replies, the puzzling part is I can get it to idle just fine so that it why I didn't suspect the idle circuit.

I think you'll find it's backing off. Mine used to, so eventually found out the ends of the spring on the adjuster were digging into the softer metals and coiling the spring, so it wanted to return to zero coil. I fitted a 6mm stainless washer at each end of the spring which helps the adjuster to turn easier and keeps the it from binding.

[EDIT], in fact if you look at your first picture it looks like the spring coils have opened as a result of snagging the aluminium.

Tornado · May 25, 2020

rvich said:
It has a tiny bit of JB Weld smeared over it now. Initially I just put a dob of RTV gasket maker on it.

I think I was adjusting to counter for the air leak when static but when dropping from a higher RPM the pilot circuit did not adjust to the change correctly as it was sucking from both the bowl and the plug area. It's a theory.

I've been chasing a weird issue where idle is fine initially, then after 20-30min riding, I get a blip in rpm as I chop the throttle closed. Have not fully worked out what is happening, so will try gooping up that blanking plug.

RoadScholar · May 25, 2020

Knowing that it can die coming to a stop, or on the decel path, can you keep it alive with the throttle? And, if you do so can you then bring it down to an idle?

Best.

o0norton0o · May 25, 2020

I would take a guitar string (high E string) and bend a 1/2" right angle in it, then raise the slides and poke out the inner and outer mixing chamber holes. When you slam the throttle closed, a strong pulse is directed at the mixing chamber hole beyond the slide to take over supplying fuel at idle. Possibly the inner hole could be compromised by accumulated dirt and impurities passing through it over time.

Maybe the forward hole helps with transition from open throttle to closed throttle in such a way that your engine can't get past that momentary starvation for fuel, but on the restart the secondary port of the mixing chamber plays a greater part in fuel delivery because the vacuum pulse is different from deceleration, so the bike starts and then idles ok.... It certainly seems like you should have both good idle and good return to idle or neither,... but perhaps it's something like I suggest that gives you one and not the other...

Either way, I poke those mixing chamber ports if I have any problems with idling to be thurough... although I haven't had any problems for quite a while...

swooshdave · May 25, 2020

RoadScholar said:
Knowing that it can die coming to a stop, or on the decel path, can you keep it alive with the throttle? And, if you do so can you then bring it down to an idle?

Best.

I can blip it to keep it going. And no, I can’t get it to idle.

swooshdave · May 25, 2020

cliffa said:
I think you'll find it's backing off. Mine used to, so eventually found out the ends of the spring on the adjuster were digging into the softer metals and coiling the spring, so it wanted to return to zero coil. I fitted a 6mm stainless washer at each end of the spring which helps the adjuster to turn easier and keeps the it from binding.

[EDIT], in fact if you look at your first picture it looks like the spring coils have opened as a result of snagging the aluminium.

I suspect this is the issue. I’m going to this next. Thanks.

@madass140

swooshdave · May 25, 2020

Mine used to, so eventually found out the ends of the spring on the adjuster were digging into the softer metals and coiling the spring, so it wanted to return to zero coil. I fitted a 6mm stainless washer at each end of the spring which helps the adjuster to turn easier and keeps the it from binding.

Ok, I think that was part of the problem.

You can see where the spring was gouging the plate.

I tried to put two washer on but the idle adjuster is too close to the carb and the top wouldn't screw down.

So I filed down one side of the washer. I don't know if this is going to work but it's worth a shot.

You can see here just how close the idle adjuster is to the carb body. I can't turn it by hand and need pliers.

I now have it running a little better. The idle was pretty lumpy and it wasn't as easy to start as I wanted. Unfortunately I didn't film all the futzing, but it was basically getting the vacuum even, starting with the slides. Then very slight adjustment to the air screws. Hopefully you can tell the difference.

jbruney · May 25, 2020

I just went through that vacuum dance with 4 carbs so it was twice the fun..... Still need to hook onto the Norton. Your 'Peril' is sounding good as well looking good.

nortriubuell · May 25, 2020

I had a similar problem last year, but running a single Mikuni. It ended up being a really small piece of the black rubber gas line, that was stuck in the float needle area. (a really, really small piece.) However, it did cause the problem, as when I removed and cleaned it ... problem gone! I will never use the black rubber fuel line again; and only use the transparent yellow marine grade fuel line now.

Fast Eddie · May 26, 2020

Sounds sweet Swoosh. Hope it’s nailed your issue...

cliffa · May 26, 2020

swooshdave said:
Ok, I think that was part of the problem.

You can see where the spring was gouging the plate.

I tried to put two washer on but the idle adjuster is too close to the carb and the top wouldn't screw down.

So I filed down one side of the washer. I don't know if this is going to work but it's worth a shot.

You can see here just how close the idle adjuster is to the carb body. I can't turn it by hand and need pliers.

I now have it running a little better. The idle was pretty lumpy and it wasn't as easy to start as I wanted. Unfortunately I didn't film all the futzing, but it was basically getting the vacuum even, starting with the slides. Then very slight adjustment to the air screws. Hopefully you can tell the difference.

Dave, I had the same issue, the adjuster is very fiddly to use ( I did mention it to Don). So while I had my carbs off I filled the original hole, drilled and tapped another one about 6mm further out, then fitted and glued a piece of aluminium offcut to the quadrant. It also means the adjuster doesn't need to be screwed in as far.

swooshdave · May 26, 2020

cliffa said:
Dave, I had the same issue, the adjuster is very fiddly to use ( I did mention it to Don). So while I had my carbs off I filled the original hole, drilled and tapped another one about 6mm further out, then fitted and glued a piece of aluminium offcut to the quadrant. It also means the adjuster doesn't need to be screwed in as far.

View attachment 16494

I remember that. I may try that too.

What exactly did you glue it on with?

What did you fill the original hole with? Did you need to do that or was it just to make it tidier?