Open throttle stalls

[s_alt]

Hey guys,

Got an R100T 81' Bike has been running a little on the leaner side and was recommended to put a little larger needle jet in. went from 2.66 to 2.68. bike is definitely not running as lean anymore. checked the sparks after a little ride and they looked much better. Not wet or black and not white. This morning as I was riding though I tried really opening my throttle was going around 70ish mph and my bike just stalled. I was able to start the bike back up again but now its not wanting to start again whereas as it happened again. Im curious if it got too much fuel? or maybe not enough? should I maybe go a little larger on the Main jet? Im curious if its running leaner on the idle jet but might of been running fine before with the 2.66 idle jet? I unfortunately don't have a socket with me here at work so I cant check to see the plugs to see how they are looking.
I check the tank to see if the vent hole is plugged but it seems clear.
Needles are positioned on notch 2. rest of the measurements are 165(main jet) -2.68(needle jet) -50(idle jet)
I put on a different straight pipe exhaust as to why the bigger numbers.
I just replaced the coils and has a newer charging system all is working well on the electrical side I would think. Just replaced the spark plugs with the proper gapping.

Any insight is much appreciated.

Thank you

 

[20774]

Could you provide your carb numbers? That will help see what was "stock".

Have you dealt with the pulse air system on the bike? How are the valve clearances...do they stay stable at the required values? 1981 was the first year of the poor metallurgy for the valve seats and over time, the valve faces become distorted.

 

[6322]

Not sure why the straight pipe but your bike may run better with some back pressure. You might consider going back to stock (exhaust, jets and needle settings), and then change one item at a time. It would be easier for you to diagnose the issue. The fact that it stalls sounds like it's flooding. Also, before changing the "needle jet", you may want to just adjust your needle position, one step at a time. Test it, see if your performance is better or worse and adjust accordingly. If it gets better, you're going in the right direction. Check your plugs to make sure you're not running to lean or too rich. I've always liked my airheads best dialed in stock, with the exception of a Dyna III, and dual plugs. Good luck.

 

[s_alt]

Could you provide your carb numbers? That will help see what was "stock".

Have you dealt with the pulse air system on the bike? How are the valve clearances...do they stay stable at the required values? 1981 was the first year of the poor metallurgy for the valve seats and over time, the valve faces become distorted.

I don't believe I have. That was a system added to help with emissions? I read somewhere about removing them or essentially plugging something up?
Carb number is 94/40/113
I just did a head rebuild about a couple months ago and lapped the valves, new rings, checked end gap. No seeping from the valves after lapping them. I just put on some new valve covers and checked the valve clearance while I was in there. everything looked good. Timing is good. carbs are synched and idling fine.

 

[s_alt]

Not sure why the straight pipe but your bike may run better with some back pressure. You might consider going back to stock (exhaust, jets and needle settings), and then change one item at a time. It would be easier for you to diagnose the issue. The fact that it stalls sounds like it's flooding. Also, before changing the "needle jet", you may want to just adjust your needle position, one step at a time. Test it, see if your performance is better or worse and adjust accordingly. If it gets better, you're going in the right direction. Check your plugs to make sure you're not running to lean or too rich. I've always liked my airheads best dialed in stock, with the exception of a Dyna III, and dual plugs. Good luck.

ha aesthetics I guess. /: I actually have a set of some reverse cones coming in tomorrow, although smaller than the stock exhaust system, there will, I think, be much more compression added back into the system. Back to square one.
I was thinking it was getting flooded too since there was no popping on the deceleration which is usually a sign on too lean and since

 

[20774]

Snowbum has an article on removing the pulse air system:

http://bmwmotorcycletech.info/pulseair.htm

Hopefully the diaphragms are OK in your carbs. Holed/cracked diaphragms contribute to poor performance at higher speeds, even though it might idle fine.

Having modified the exhaust, you have deviated away from what the BMW engineers were hoping for. Usually changes in the exhaust is a zero-sum game...it might help in one region but hurts in another.

You have definitely gone richer all the way around. Not sure of the steps you have taken to get there, but typically you should make one change at a time and assess the results. Maybe even make a change and if no difference, put it back the way it was and make another change. That way you can get a sense of what is doing what in the carbs. You should do a plug-chop to assess the performance. Do it in a safe place where you can run at a constant setting for 2-3 minutes, close the throttle, quickly turn off the bike, and coast to a safe stop. Then look at the plugs.

 

[s_alt]

Snowbum has an article on removing the pulse air system:

http://bmwmotorcycletech.info/pulseair.htm

Hopefully the diaphragms are OK in your carbs. Holed/cracked diaphragms contribute to poor performance at higher speeds, even though it might idle fine.

Having modified the exhaust, you have deviated away from what the BMW engineers were hoping for. Usually changes in the exhaust is a zero-sum game...it might help in one region but hurts in another.

You have definitely gone richer all the way around. Not sure of the steps you have taken to get there, but typically you should make one change at a time and assess the results. Maybe even make a change and if no difference, put it back the way it was and make another change. That way you can get a sense of what is doing what in the carbs. You should do a plug-chop to assess the performance. Do it in a safe place where you can run at a constant setting for 2-3 minutes, close the throttle, quickly turn off the bike, and coast to a safe stop. Then look at the plugs.

Im hoping with the although smaller reverse cones that it might bring it back to stock with maybe slight mods but definitely starting from scratch would be a good plan.
Ill give that a try. Thank you. ill make sure to report back to you guys when I get a look at the plugs from that testing.

 

[Anyname]

It could be totally unrelated to the jets. There could have been a fuel blockage or even a bad electrical connection. You know the old saying, "when something fails, check the things you worked on last".

 

[s_alt]

It could be totally unrelated to the jets. There could have been a fuel blockage or even a bad electrical connection. You know the old saying, "when something fails, check the things you worked on last".

I thought it might of been a fuel blockage maybe from my petcocks but I have filters and can see the fuel running through.
I did however just put in a larger needle jet from 2.66 to 2.68 cause it was running lean in the early to mid throttle position. I might try and set my needle down one so it has the larger needle jet and main jet but a tighter taper with the needle. idk. I was going through my bing book a little last night. Im pretty certain I was getting way to much fuel at the higher revs even though my 1/4-1/2 throttle positions was ripping! So it kind of fixed the issue except going past that mark. ha maybe a smaller main jet?

 

[jimwjarmour]

rich carb settings

Hi, have run my 1977 r100s with opened up exaust and perfomance cam light flywheel Dyna ign special plugs etc and never had to go that rich ,45 pilot 2.66 needle position 3, 165 main jet ,now without the sports cam in I am running 45 or (40 hard starting while cold but very lively when warmed up ) pilot 2.66 needle jets position 3 and 160 main , I would start with checking diaphrams then float levels, and any airleaks around rubber carb to head tubes,hope this assists Jimmy

 

[s_alt]

Hi, have run my 1977 r100s with opened up exaust and perfomance cam light flywheel Dyna ign special plugs etc and never had to go that rich ,45 pilot 2.66 needle position 3, 165 main jet ,now without the sports cam in I am running 45 or (40 hard starting while cold but very lively when warmed up ) pilot 2.66 needle jets position 3 and 160 main , I would start with checking diaphrams then float levels, and any airleaks around rubber carb to head tubes,hope this assists Jimmy

damn. Is the needle positioned a little richer for you in this case? Mines suppose to be on the second notch. Maybe I should go back to the original settings and bring the needle up a little to give it more flow.
Checked the float bowls yesterday and all was good. I did notice that the left carb when adjusting the idle mixer screw that i could back out quite a bit without it wanting to stall /: it was however making the idle change or if I fully closed it it would stutter and eventually stall. It makes me think that you're right and there might be an air leak somewhere. I sprayed ( at least i think this is how its done) carb cleaner around it to see if anything happened but nothing. maybe i'm doing it wrong ha.

Thanks man!

 

[jimwjarmour]

carbs

Hello again, when you say one side does not respond until nearly out, I would give the carbs a really good clean while off the bike spray the little holes each side of the butterfly you will see they run from the rear portion of the carb blow through this with all the jets out to make sure its clear , check the o rings on the jet block, pilot jet and mixture screw 1 1/2 turns out would be about right ,once you get it right try a 264 needle jet if you ride in the mountains, 1981 bikes ran needle position 2 for emissions and a 160 main, well best of luck let us know how it is going, Jimmy

 

[toooldtocare]

In 1998 I bought a used 1995 R100RT that the previous owner tried to improve on. The bike only had about 3,000 miles on it. He wanted more air/fuel so he replaced the jets, raised the needle valve, and installed a K&N air filter. He also wanted less back pressure so he cut open the resonator, removed the guts, and welded it back together.

When I bought the bike it would barely hit 90, got about 30mpg, and sounded trashy with the open resonator. It would also stall if I opened the throttle more than 3/4 way. I put everything back to stock. Immediately the performance improved. In West Texas I could easily hit 100+ mph plus, use full throttle, and the mpg increased to 45. In other words, the bike ran like it was suppose to.

It sounds like you are on the right track. Sometimes stock is better, unless you really know what you are doing. Most of us, including me, don’t.

 

[s_alt]

Update:
Since I didnt have my carb synching tool with me at work I wanted to back track to when the bike was running and put the smaller jet (2.66) back in tightened and cleaned anything that had ports. checked o rings. except the throttle body one. The bike would run a little and fine except when coming to a stop the bike would just die though at idle it was fine when i started it up and after checking the mixer screws. After trying to start it too many times my battery was drained so I have it now on the tender. I recently hooked up a new speedo/tacho and notice the wire getting really hot since its a tacho speed converter. my fuses are still intact but idk maybe that is shorting something. The dying at a stop coming from riding is new though. Maybe its my valves? did i not tighten them all the way and they tightened more? 10-15mm on intake and 20mm exhaust. once the battery is charged back ill get back at it. maybe recheck the valves again.

Thanks everyone

 

[20774]

I'm sure you meant to use a decimal point, but the valve clearances are 0.10/0.15mm intake and 0.20mm exhaust. Definitely check them to be sure they're still where they should be.

You might need to redo the synch if you took things that far apart.

 

[s_alt]

Update:

I did mean .10mm ha thank you.

So i put the stock jets back in but brought the needle to the third notch to make it a little richer. Didnt notice much of any difference in performance then before but instead I got a really loud bang/backfire and then stall.
I believe i found the issue though not with what I was talking about before.
I put on new fuel filters and I think they were creating some sort of air blockage or something even though fuel was going through it I think when opening the throttle the fuel wasn't flowing quick enough maybe and then id get a super loud backfire and then stalled. I removed the filters and it seems to be riding okay now. Im still having a hard time with the left carbs idle mixer screw. Maybe its the intake manifold that's sucking in air? It still is running on the leaner side whereas the right seems to be good. I cleaned the left one once again making sure all the passages were flowing. float bowls were both good. I even put in a larger needle jet to see if that might compensate for the air. nothing different it seems.
anyone have any experience with getting these intake manifolds off? they look like a pain in the butt to get off.

 

[20774]

So, you do have the right amount of fuel in each float bowl? Should be something a little over 1" in height in the bowl.

As for the intake spigots, there was a write up by Oak in the latest Airmail. His method for removing them is to take the heads off and use an oven to heat the head to 350 degF. Then you stuff a cold, wet sponge into the spigot and use a pipe wrench to remove the spigot. Installation involves using blue Loctite and Hylomar with the spigot being cooled in the freezer. Then reheat the head in the oven and when at temp, quickly put the spigot in place.

Snowbum has a slightly different approach...looks like his way leaves the head on the bike...near bottom of this page:

http://bmwmotorcycletech.info/break-in.htm

 

[jimwjarmour]

me again

hello,again, you say you checked the float bowls,its the float level thats important with the bowl off hold the float up and check where it touches the float needle ,the floats should be level to the carb body,you can do this with the fuel tap on and see where the gas stops and starts flowing the float level could be too low on that side causing a low level, and cutting out on that cylinder when stopping ? I wouldnt touch the carb spigot perhaps run some locktite around the threaded part to the head ,yes check the valves when cold ,hope this assists Jimmy

 

[s_alt]

Hey guys,
thanks for the responses.
Correct. I do indeed have the right amount of fuel in the float bowls after pulling and measuring them. I actually noticed yesterday ( with the carb still attached) when pulling the float bowl it wouldn't really stop dripping even with the petcocks turned off. not pouring out but dripping. the right wasnt doing that at all. Maybe my left petcock has a leak? idk
I did just do a full carb rebuild about winter time this year and it didn't get ridden all too much but I cant recall the left carb having these troubles when tuning them.

going to try and spray some carb cleaner around the area to see if there's a leak but didn't notice anything before when trying this test.
Ill throw on some loctite around the spigot to see if that changes anything.

Thanks again guys!

 

[20774]

The leaking petcock is really only a problem if your floats don't shut off the flow of fuel into the bowl. Once the fuel level gets high enough, the seat should close it off. But a leaking petcock and a malfunctioning float could spell disaster if the bowl overflows into the intake track, past an open intake valve and into the combustion chamber. Then it either slips past the rings to dilute the gas or in a really bad situation, creates a hydrolock condition the next time you hit the start button...bent rod.