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R60/2 .... Backfires on left carb issue

metoo
Posts: 21
Joined: Mon Apr 17, 2023 11:27 am

R60/2 .... Backfires on left carb issue

Post by metoo »

Hi everyone,

I have an issue with my 1968 R60/2 : I have backfires thru the left carb. If I twist the throttle at once, the engine will die, and If I twist it slowly then I have backfires.

What could be the cause for this issue?

The carbs are 133,134 bings and are cleaned with new seals (they have 115 main jets and needle is set to 2nd hole)
New spark plugs
New coil
New wires
New condencer
New points
New airfilter
Static timing set

Anyone have any idea what could be the problem?

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schrader7032
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Re: R60/2 .... Backfires on left carb issue

Post by schrader7032 »

Did this happen in the past? What recent maintenance has been done?

I'd start swapping things from left to right and see if the problem switches sides.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

metoo
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Re: R60/2 .... Backfires on left carb issue

Post by metoo »

schrader7032 wrote:
Thu May 18, 2023 12:47 pm
Did this happen in the past? What recent maintenance has been done?

I'd start swapping things from left to right and see if the problem switches sides.
Well, It's new purchase. I don't know the bike history... the bike was in storage for more then 10 years, and now I'm tiring to bring it back to life.

BTW, I've checked compression, left side is 130, right side is 105

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schrader7032
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Re: R60/2 .... Backfires on left carb issue

Post by schrader7032 »

That's not very good compression...too much of a difference. You said you checked the static timing. Have you looked at timing with the engine running at idle?

You might check the safety gap of each spark plug wire at the coil underneath the front cover. The wires are screwed into a post on the coil. There are triangular tips at the base of the coil that are near the ends of the coil wires. The distance between the tip and the coil wire is supposed to be 10mm. Possibly if the distance is less, the spark could jump the gap and then later when it picks back up again, there's excess charge in the cylinder and it goes off.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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Re: R60/2 .... Backfires on left carb issue

Post by 808Airhead »

Are you meaning "popping in the carb" at idle? "Backfiring" is when the explosion happens after exhaust valve/in the exhaust and is usually a very loud "pop". If it is "popping at idle" look for low compression/bad rings/as well as poorly sealing valves, everything else being correct of course.
Thomas M.
R69S - R60/2 - R67/2 - R51/3 - R69

metoo
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Re: R60/2 .... Backfires on left carb issue

Post by metoo »

I've looked at Bing's spec charts and noticed that my carbs should have 110 main jet and needle pin set to 3rd hole.
My carbs have 115 main jet and needle set to 2nd hole.
Could this be the problem?

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schrader7032
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Re: R60/2 .... Backfires on left carb issue

Post by schrader7032 »

Needle in 2nd hole would cause the bike to run leaner at regular speeds. The main jet really only comes into play once you get to higher throttle settings, like greater than 60 mph.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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Re: R60/2 .... Backfires on left carb issue

Post by jwonder »

Hello, let’s see if we can help. Following is what I would do.

1) I would put the carbs back to spec on the needles, jets, etc. by the way needles do wear.

2) check everything; like the points gap, safety gap and dynamic timing, etc.

3) does this happen hot and cold or just hot? I just had a brand new coil quit on me after about 200 miles. So don’t trust anything even if it’s new, maybe especially if it’s new.

4) check valve clearance.

5) check for exhaust leaks.

6) compression is a bit low but was that hot or cold? I find compression changes greatly based on who is doing the checking.

Report back and let us know. I hope this helps.
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

metoo
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Re: R60/2 .... Backfires on left carb issue

Post by metoo »

Update:

Today I've try this:

1) setting valves gap - problem remains
2) trying 2 coils, one used original bosch - reads no resistance between leads ports (1), other one new emerald island - reads 60,000 ohms (exactly :shock: ) between leads ports - with both the problem remains
3) setting the jet needle to 3rd hole - problem remains

I've ordered new jets and spark plug caps from EME, once they arrive I will install them and report

metoo
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Re: R60/2 .... Backfires on left carb issue

Post by metoo »

So, today I have time to check timing again. I manage to get strobe light and found that my timing is way retard...
I've rotate the points plate clockwise, as much as I can, only to get spark at OT mark.
I've started the engine and all popping and banging are gone !

So, I guess my problem was timing... but still... the points plate is at max clockwise rotation and still I can not be at S mark, only at OT mark. Is there any more ways to set timing, or should I just enlarge the screw holes so the plate can have more rotation?

Also, I've manage to brake the lobe felt. Is it replaceable?

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