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Old 11-29-2012, 08:20 AM   #1
lucky23 OP
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R75 bogging down...

Hey Guys! My 1972 R75/5 runs fine, but when I give it a twist while riding it seems to bog down. I have to back off the throttle a bit and let it catch up. It gets a little better after she warms up a bit. It SEEMS to me to be exhibiting a rich condition, but I'm not sure...any comments? Thanks for looking!
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Old 11-29-2012, 08:57 AM   #2
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Trend or event?

You will get a number of requests for more information. History? Daily rider? Sat for a long time? Just started doing this? Kinda did it but became worse? Chokes opening and closing properly?
My gut tells me that you have carb issues, specifically diaphragm. If the history of the carbs is unknown, then it is a good bet they could use some love. Gasket kit , needles and needle jet, float needle, and possibly floats.
Of course we are assuming your valves are set properly, has compression, it is timed to a tee and the carbs are balanced.
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Old 11-29-2012, 09:24 AM   #3
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Is this a new symptom?

The tune up is indicated. Start with setting the valves. Then check or set the timing, points? Check dwell. After 1 & 2, that is, after Valves, then Timing, you can move onto setting the carbs.

Carbs are tuned after a 10 to 20 min warmup run. The bike should not be allowed to idle on the center stand for too long, say more than 4 mins. If you have a large box fan to set in front of the bike this will keep the engine cool.
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Old 11-29-2012, 09:42 AM   #4
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No, it hasnt been sitting. I ride it a few times a week in the winter, daily driver in the summer. I havent adjusted the valves in a few months. I rebuilt the right carb because it was leaking, but not the left. Chokes seem to be working fine. Havent checked the timing...
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Old 11-29-2012, 10:13 AM   #5
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This could be several things. So to proceed in an orderly fashion we would like the bike to be at some sort of standard, a state of tune. Mykill says carbs, maybe. It could also be timing but more specifically the dwell angle.

It is hard to gap points once they have been used a while. But if you will check the timing and find it is slightly retarded this is because the points have closed a small amount. With out adjusting the breaker plate but opening the points a tiny amount the timing can be brought back to where it belongs you may find the problem is alleviated.

Points always wear. There is an initial wear in and then they should be stable for sometime afterwards. Years ago we filled the contact points but this is not recommended anymore because the Tungsten coating is so thin. Too bad because the transfer of metal from one contact to the other causes a hill on one side and a valley on the other. This is almost impossible to use a feeler gauge gaping tool on.

If the timing can not be brought back to the correct setting this way you may just need a new set of ignition points. This gets expensive, like everything else today prices are going up. But many of us recommend you use an ignition Booster. Not a full electronic ignition system conversion but the Booster uses the points and the mechanical advance system but the points will last a long time because the Booster takes the high Voltage off them.

Lets try to get it running for now. Later somebody will tell you about what you can do to make the points last longer.
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Old 11-29-2012, 05:46 PM   #6
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Thanks, I will definitely check the points and report back.
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Old 11-30-2012, 04:05 AM   #7
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Silly question I know but when was the last time you changed the air filter ?
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Old 11-30-2012, 05:15 AM   #8
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Did you balance and tune the carbs after the rebuild?

Did the symptoms start after you rebuilt the carb?

IMHO, it sounds like it's running rich. Here's a quick test to see:
1. Warm up the bike
2. Pull the air filter and run the bike. If it no longer bogs, the carbs are too rich with the filter in place. You're adding more air by removing the filter.
3. If 2 doesn't work, slowly turn on the "choke". If the bogging stops, you're carbs are too lean with the choke off.

This may help you figure out which way to go to fix the problem. I'd also check for air leaks around the carbs (warm up bike and spray carb cleaner or WD40 around the boots, it'll change the idle speed and smoke if the cleaner or WD40 gets pulled throught he engine) and pull the diagrams and check for hard rubber or a hole in the rubber.
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Old 11-30-2012, 10:11 AM   #9
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This is a /5. Has Type 57 (or 53?) carbs therefore no diaphragms. Also has "tickler" and not "enrichener". At least that's the dark alley my mind sent me down just now. Someone will correct me on this, I hope.
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Old 11-30-2012, 10:32 AM   #10
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But it's an R75/5. They don't have diaphragms?

I think they do, Bill.

Lucky, We need the numbers on the sides of your carbs, please.
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Old 11-30-2012, 10:39 AM   #11
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I dunno Charlie. Is there a diaphragm in here somewhere?

http://www.bingcarburetor.com/pdf/T53x.pdf
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Old 11-30-2012, 10:49 AM   #12
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According to the Bing Book the type 53 carburetor is found on an R50 or R60/5. It is also found on these size bikes in /6 and /7 years. The bike in question is an R75/5. Uses a type 64 carb;

(I'll see your pic;)

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Old 11-30-2012, 10:56 AM   #13
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Didn't the early /5 CV carbs omit the slide spring?

That could cause a rich bog on throttle.
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Old 11-30-2012, 11:01 AM   #14
Horsehockey
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Quote:
Originally Posted by disston View Post
According to the Bing Book the type 53 carburetor is found on an R50 or R60/5. It is also found on these size bikes in /6 and /7 years. The bike in question is an R75/5. Uses a type 64 carb;

(I'll see your pic;)

I stand corrected. I was thinking about a buddy's /5....must've been an R60.
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Old 11-30-2012, 11:05 AM   #15
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Quote:
Originally Posted by ignatz72 View Post
Didn't the early /5 CV carbs omit the slide spring?

That could cause a rich bog on throttle.
My 1975 /6 came with "late" /5 carbs and therefore they have no slide springs. I think no springs can enhance idle creep (slow return to idle) but I don't think it's related to a higher rpm bog. Charlie will correct me on this misunderstanding shortly.
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