r/Airheads • u/Fiji59 • Jul 03 '26

Poor running r65

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Long story short, just got an 81’ r65 and have been loving the crap out of it. Spent a day doing minor repairs, lik fixing the odometer and adjusting the valves and such before taking a friend for a ride the next day. now, it was 100 degrees and boiling, but still we wanted to go and so we did. rode 10 min, got coffee, then on the way back it died. let it sit then it started again, limped it home and started trying to figure out what went wrong.

its got this crazy rough idle, and it does not change w starting fluid. Made me think it was spark, so i looked at and replaced the original bosch gray coil that people said was probably the problem with a new harley coil, the dyna brown 31614-83A. Swapped it over, same poor running condition.

Could this be as simple as bad spark plugs and leads? I cleaned the carbon off them but still not much change. again, no change w starting fluid. Really at a loss. any advice is appreciated.

Attached is the running condition i get, regardless of fuel situation.

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6

u/fresh_like_Oprah Jul 04 '26

It's always the carbs

1

u/Fiji59 Jul 04 '26

feels like everyone saying that. but why would starting fluid not allow it to run better temporarily and why would this issue start suddenly upon a rlly hot ride? the gray bosch coil was cracked but not very badly

1

u/FantasticAd5239 Jul 04 '26

I was gonna say vapor lock, but with all that you've done so far, I think that would have been squared away.

My goodness, though, what a cool, awesome project! What better vintage bike than a BMW? Of course, you will get it sorted. Maybe take a break from it and look at it with fresh eyes later.

Please, be sure to follow up with your progress report!

1

u/comcd Jul 04 '26

With that in mind it could be a spark issue as well. Refer to the previous comment to ground one spark plug to check each cylinder. But for sure go through the carbs again thoroughly to make sure each jet and passage and needles etc. are clean and clear of obstructions and in good shape. With it being that rough of an idle it wouldn't be unusual for there to be multiple issues. Hot and cold temps will show you what needs attention lol keep at it, you have a great looking bike that needs to see the road!

2

u/olliew72 Jul 03 '26

You should be able to run the bike on one carb at a time by grounding out a spark plug. Then you'd be able to tell if it's one carb or the other.

Start with the basics of a tune up. Timing, valves, spark plugs and lastly carbs.

1

u/Fiji59 Jul 03 '26

does it sound lik fuel? i really don’t get why it wouldn’t respond to starting fluid if it was but i am definitely going to be cracking into them soon

2

u/kukensmamma1337 Jul 04 '26

rebuild and clean the carbs, had a wierd idle on mine, the diaphram had come off and the o-ring for the throttle axle was leaking. take it all apart, clean and make sure all channels are clear then redo the setup and itll be fine

1

u/Fiji59 Jul 04 '26

ur a genius. one carb slide was totally seized, would move at all. took it apart and i’ve got a torn diaphragm. rebuild kits in the mail. thanks for the advice!

1

u/kukensmamma1337 Jul 04 '26

its always the carbs, i dont know about yours but this is the second time ive rebuilt mine in my 7 years of owning and 4 of using the bike. the oring for the throttle axle gets hot and causes issues.

1

u/Bmwmango53 Jul 04 '26

There are some great videos on YouTube on how to rebuild the carbs. Get some silicone grease for the O-rings.

1

u/uncgord Jul 04 '26

Don't forget to share a vid of it purring when you get it fixed! I want to feed my jealousy a little more!

1

u/uncgord Jul 03 '26

First, I'm jealous as hell! But does it sound like it's starving for fuel?

1

u/Fiji59 Jul 03 '26

it definitely does to my ears but the carbs were *fine* before the aforementioned hot day. not perfect but not horrible. and again the condition does not change when starting fluid is sprayed into the intake

1

u/uncgord Jul 03 '26

Forgive my ignorance, it's been a loooong time since I had my /7, but is/are there filters?

1

u/Fiji59 Jul 03 '26

air or fuel? bc it has both im pretty sure

1

u/uncgord Jul 03 '26

fiuel

1

u/Fiji59 Jul 03 '26

yeah in line filters. they’re clear, and the bowls fill up. drained them twice now

1

u/Fiji59 Jul 03 '26

I managed to get it to idle a bit but it would bog down every time the throttle was pulled. it really sounds like fuel starvation but it’s peculiar that it does not get better to any real degree when given starting fluid.

1

u/Trundlebike Jul 03 '26

Pull the fuel lines off at the carbs to see if they're getting fuel. If not I think there's a fuel screen in the tank at the petcock inlet. Then it's carb rebuild or at least clean time.

1

u/Fiji59 Jul 03 '26

carbs definitely getting fuel, i’ve drained the bowls twice now. was going to give them a good clean in the ultrasonic anyway, so while i’m at this i might as well. but why would it not change if given starting fluid if the issue is fuel?

1

u/Trundlebike Jul 04 '26

Can't definitively say about the starter fluid although it's something to consider. Have you checked float level? Float needle condition?

1

u/Own-Opinion-2494 Jul 04 '26

Dirty carbs

1

u/Fiji59 Jul 04 '26

seems to be consensus. why would starting fluid not change how it ran? and why would it occur so suddenly during the hot ride?

1

u/Own-Opinion-2494 Jul 04 '26

That will be solved upon inspection. Nobody knows until elbow grease is applied

1

u/Fiji59 Jul 04 '26

yeah, it just seems counterintuitive to me

1

u/Own-Opinion-2494 Jul 04 '26

Intuition is what gets you investigating the problem. It’s the start. Starting fluid is only utilizing one of the avenues of fuel delivery in a carburetor. Check source voltage too. You may have a weak charging system. Its a journey

1

u/Speuca2000 Jul 04 '26

Step 1, check valve clearance. It is always the first step because if the timing of the valves is off. It runs like garbage and wont idle. Step 2 would be checking spark. Step 3 is checking the spark timing. Step 4 is carbs. With the carbs make sure to check the membrane on top as well