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Topic-icon My R75/5 sputters at 75 MPH

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2 weeks 6 days ago #3693 by Cliff
Cliff created the topic: My R75/5 sputters at 75 MPH
I ride a 72 R75/5. It rides smooth as can be. Since I own it, three summers now, on the highway just at 75 MPH is starts to sputters. Almost as if it has a governor on it. I don't believe it happens in the lower gears, even as I rev it to 5,500 RPM. The only time I feel it is at the highest end of fourth gear. The pattern is a cycling of power giving a feeling of being starved of fuel but I don't think that is it, cause it is only in fourth. I thought it may have been a timing issue but I have already replaced the points with electronic ignition. The engine has additional power but somewhere there is a bottleneck in regard to power.
Does anyone have any thoughts on this? I always feel one of you veterans have usually traveled passed these issues somewhere in the past. Thanks for looking in on this, Cliff

Keep the wind in whatever hair you may have left!!

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2 weeks 6 days ago - 2 weeks 6 days ago #3694 by tpeever
tpeever replied the topic: My R75/5 sputters at 75 MPH
Plugged main jets? Do you have inline fuel filters? Could these be restricting fuel flow?
Last Edit: 2 weeks 6 days ago by tpeever.

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2 weeks 5 days ago #3695 by Wm.
Wm. replied the topic: My R75/5 sputters at 75 MPH
I had a similar problem at around 80 mph about 6 years ago. I bent the floats to where they should be and that solved the problem. Maybe take a look at where your floats are sitting/how much fuel sits in the bowl when you remove it (of course the bike would need to be on the center stand). I hope this helps!

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2 weeks 5 days ago #3698 by Cliff
Cliff replied the topic: My R75/5 sputters at 75 MPH
Thanks so much. I will break my carbs down and combine both the suggestions I have received so far. Clogged ports and misaligned floats. Both are very possible from that putz that rebuilt both my carbs.................ME!!!!

Keep the wind in whatever hair you may have left!!

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2 weeks 5 days ago #3699 by tpeever
tpeever replied the topic: My R75/5 sputters at 75 MPH
Wm's suggestion about float height is a good one. There should be a specified height in the manual. Do also check for any restrictions on fuel flow like clogged filters on your fuel taps inside the tank, crimped crossover pipe or clogged inline fuel filters if you are running those. I think I would start by flushing out the tank and go from there. It sounds like you don't have sufficient fuel flow at more open throttle settings so anything restricting fuel flow along the path may be the culprit. Please let us know what you find out!

Tobin
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2 weeks 4 days ago - 2 weeks 4 days ago #3702 by Wobbly
Wobbly replied the topic: My R75/5 sputters at 75 MPH
If you are in the USA, then the Number 1 suspect is ethanol fuel.

Set Up
But first you'll need to do some initial work to make sure we are chasing the correct demon. Don't worry, it's VERY inexpensive. But also VERY necessary...
Strobe time your engine at VERY HIGH rpm using the "F" mark. Your install manual probably gives an RPM range, so follow that. If not use 5000 RPM.

• Install new metal core plug wires along with new NGK 5K Ohm resister plug caps.

• Install 2 new NGK BP7ES plugs with lubrication on the threads.

• Install a new air filter.

Carbs
I agree it sounds exactly like a lean condition. That can be caused by many, many things... air leak, low float level, torn diaphragm, or varnish-coated jets. You gotta check them all...
• Remove the carbs from the bike.

• Withdraw the slide and inspect the diaphragm for holes. Inspect the needles for any sign of varnish, pitting, wear or corrosion. They must be perfectly smooth under magnification. Not all the older needles are brass, so they may appear to be Parkerized. If there is any doubt about their surface quality, then order a new set. Install those with the exact same exposed length, which should be identical for both sides.

• Check the float level with the carb body so that the gasket surface is in the vertical position, pivot at top. Allow only gravity to push on the spring loaded float needle.

• Replace any jets that have a brownish varnish appearance. Replace the 2 main jets regardless.

• Reassemble and reinstall the carbs with 2 new intake rubber hoses.

Treatment
Buy a bottle of StarTron fuel treatment and start adding 1oz to every tank full of High Test fuel you buy, until the bottle is used up. Home Depot, boating supply stores, and lawn and garden supply stores sell this stuff. It's easy to find and nothing else works as well.


Somewhere in there, things are going to get better.

Don't hide 'em, Ride 'em !!
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Last Edit: 2 weeks 4 days ago by Wobbly.
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