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Beezer Josh 07-25-2013 07:35 PM

Back in late January I picked up an R75/5. I really like the bike. It runs well once it's started and it's way smoother than my BSA, especially at higher speeds! However, I've always had a problem starting it even with the enrichener and the problem gets much worse in lower temperatures. With that in mind, I rebuilt and rebalanced the carbs. I replaced all the jets, making sure all circuits were open. I balanced them with a TwinMax, tuning the idle mixture in the middle of the mixture screw's very narrow in/out range. I also checked the valve adjustment. The left intake and right exhaust were slightly off, but only by very little-about a thousandth. I also replaced the battery.

Next I went to adjust the points. Lo and behold, the PO replaced those with a Dyna III. The timing was off-too advanced at idle, too retarded at 3k. So I replaced the advance springs, which fixed the problem. Timing is almost spot on, with a little ghosting.

The idle was still off so I added the springs to the slides as Snowbum suggests. No difference, so I took them out. A few weekends ago I replaced the timing chain, tensioner, tensioner spring, and crankshaft and camshaft sprockets and re-timed the bike. No change. I figure the ghosting I should be able to adjust out by moving one of the pickups on the Dyna III. Argh! I think the starter also needs to be rebuilt, but, taking the starter out of the equation, it's still a bear to start with the kickstart. I'm not sure if this is normal, but it seems like it wants to fire on one cylinder while starting it. Kinda like a whir-whir-whir-boom-whir-whir-whir-boom. So, I'm now begging you guys to give me some more ideas on what else to check.

mykill 07-25-2013 08:14 PM

Assuming you have torqued the heads and set the valves properly, I would verify the state of the coils, wires and caps. New plugs may help too.

Warin 07-25-2013 09:23 PM

Carb starter circuit? One working the other not.

For better battery start up performance an odessy battery would be good. But it is an add on.

Bill Harris 07-26-2013 03:27 AM

That is what I'm thinking. Especially the little jet in the bowl and the pickup tube. And make sure that the enrichener discs are correct R and L.


Beezer Josh 07-26-2013 03:50 AM

Thanks guys! Just to add to the list, one of the first things I did was change the plugs.

When I cleaned out the carbs, I made sure that the jet in the bowl and the pickup tubes were clear. In fact, I thought that might have been an issue, so I cleaned the carbs out again. At that point, I also verified the enricher discs were on the correct sides (I only did one at a time, anyway) and that the jets drilled in the discs were clear and operated in the correct positions.

On maybe a related note, once the bike warms up, idle varies by about 100-150 rpm. Sometimes I'll pull up to a stoplight and the idle will be very slightly faster than at the previous stoplight. I have also checked for air leaks around the flanges and that came up negative. All o-rings are also brand new.

AntonLargiader 07-26-2013 04:32 AM

Did you set the idle mix screws with the engine hot? I can't see why it would want to hunt by 150RPM when hot if you set it while hot.

Sounds like you've done all of the right carb stuff. Have you done a leakdown or compression test?

That bike should start like a dream.

Bill Harris 07-26-2013 05:05 AM

Agreed, he has done the right stuff, both with carbs and engine tune. Admittedly, it won't cold start as well or idle as consistently as a fuel injected, computer-controled engine, it ought to start better ( and I would't sweat a 150 rpm idle variation).

At least you've eliminated the obvious. Time to put away Occam's and look at compression/leakdown and other esoteric things...


Beezer Josh 07-26-2013 05:24 AM

I set the idle mixture after about a 50 mile ride. I figured that should be enough to warm up the bike.

I have not done a compression or leakdown test. That'll be next on my list of things to try. I'm also not sure how old the spark plug wires and caps are, and the coils are original. I've been told that 95% of carb issues are electrical anyway. I'll do some initial electrical tests later this morning and see what I get.

Pokie 07-26-2013 07:57 AM

Josh, you didn't state what year the R75/5 was. The early R75s (1970 and early 1971) had some carb and advance issues. The carbs leaked water and air through the pressed in disk on the carb tops.

They also had issues with the intake tubes not being molded quite right, partly covering the holes on the back of the carbs. Just for fun, have you checked the air cleaner?

The right carb mixing tube has a habit of collecting water on top, between the mixing tube and the nozzle. This water needs to be removed manually, it will not just get sucked through the carb, this water also causes a hard start situation. The water in the right carb gets there from the engine breather dumping into the right intake tube.

The hunting is usually ignition.There have been a few different advance mechanisms over the years as well as heavier springs to help stop this problem. On the earlier bikes, we not only had to put on heavier springs but we also had to shave the bob weights. After your advance mechanism is on and tightened (don't over tighten), check the movement of the cam and bob weights. when you spread the bob weights and let go, do they snap back or just sort of move back to the closed position? They MUST snap back and the cam must move freely!

I'm not familliar with the electronic ignition you have so I can't help there.

The ghosting is common. You can illiminate some of that by tapping the end of the cam one way or the other to bring it in but the next time you remove the advance mechanism, it will likely be back.

One more thing to keep in mind, on the slide carbs, it's an air mixture screw. On the CV carbs (like yours) it's a fuel mixture screw. So, adjust to find it's best running at idle, then back out the screw about 1/8 of a turn to assist with cold starting.

Beezer Josh 07-26-2013 09:55 AM

Pokie, the bike's a '73 with the later /9 and /10 carbs. Air cleaner is good as I changed that at the same time as the spark plugs. The bob weights also snap back quickly, so I don't think those are an issue. I've also tried backing the mixture screw out previously, and still no change.

My coils tested well, and the resistances are within the range of those listed in the Clymers manual. One thing I did notice was that my spark plug wires showed some resistance. The left showed 1.011K while the right showed 0.980K. Should these be 0 resistance wires?

Bill Harris 07-26-2013 10:17 AM

The plug wires are stranded copper and should have zero resistance. Pull 'em off at the coil and see if there is corrosion in the coil tower. The coil terminal, from the factory, is actually soldered (not crimped) to the coil wire. The plug connectors are the resistor type, stock has a resistance of 1K ohm, but the later 5K ohm connectors will work. The plugs, of course, are non-resistor type. I like NGK BP7ES (or BP6ES).

FWIW, you may know this already...


Beezer Josh 07-26-2013 10:26 AM

Well that's interesting, Bill. When I got the bike, I changed the spark plugs and replaced them with the same type I pulled out: BPR6ES. It appears that my plug caps test out fine at 1k, but I'm also using resisted spark plugs. I'll go buy some non-resisted type and see where that gets me. If it messes with the EI, I guess I can always switch back, or at least I can have some fun with people's car radios!

disston 07-26-2013 02:56 PM

Don't need resistance plugs. You have resistance caps. But this may have zero effect.

Immediate and energetic starting is something I have insisted on for several years. I always set the enrichners to full on, unless the bike is already warm, and crank the throttle open about 1/3rd. This time of year the enrichners come off right away, when colder out they come off slower, but I still use full enrichner in the Summer. I don't spend a lot of time warming the bike before riding but I do spend some time warming the bike. Minimum I'd say a minute. Maximum 2. Warm up is held on by the throttle cruise control screw. I set to a comfortable 1500 to 2000. I have to control the idle with the throttle for the first 5 minutes or more.

I do have problems with idle once my bike is warm but it has very little to do with starting the bike.

AirGsPd 07-26-2013 03:56 PM

Somehow mine has good and bad days. Most of the time I set the enricheners to half and the bike starts right up. Then on other days I have to play with the enricheners and / or the throttle to get it started. Once it has started it runs like a charm... Typically I take the enricheners off as soon as I am on my way and accelerate easy to warm the engine up first. To me it seems kinda odd that it so inconsistent. :huh

Mista Vern 07-26-2013 04:28 PM

It may pay for you guys with problems to check the enrichner gaskets. Not uncommon for them to succumb to vacuum forces, and once that happens all kinds of mystery problems occur.

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