Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

Add to My MSN


Tech Corner 

Bonneville carburetors

Q: Can you give me any advice on carburetors for my 1970 Triumph Bonneville? Right now the bike is using Amal 930/43-930/44 carbs, which I believe are worn out. Do you know which new ones will fit the bike? Would it be the 930/9 or will the 930/300-930/301 premium be better? — Graham Rashleigh, U.K./via email

A: I’m a big fan of using original carbs on these bikes. That way someone else has taken the time to figure out the jetting and slide cutaway. With that in mind, the Amal carb website shows either the 930/43-44 standard carbs or the 930/43-44 premium carbs for your model Bonnie. ACK145 is the carb set for the standard and PACK145 is the premium set. I like the features of the premium carbs — improved metallurgy, improved idle circuit and stay-up floats — but you do have to consider the extra cost. A less expensive option I’ve used here in the U.S. is having the carbs sleeved. I don’t know of any firms offering that in the U.K., however. Here it costs about $100 per carb to have the bodies bored out and the slides turned down and sleeved with stainless steel. That brings them back to original tolerances and removes the sloppy fit of slide to body. Having dissimilar metals in the body and slide then reduces the rapid wear you get from the original setup. MC


Tech Corner

Triumph clutch troubles

Q: I have a question for you regarding troubleshooting the clutch on my 1973 Triumph Trident 750. I have recently replaced the clutch plate. When riding the bike I cannot shift into neutral, and when stationary with the clutch pulled in the engine is still engaged. I have adjusted the clutch lever and the main clutch nut under the circular clutch plate cover. Should the clutch nut be loose enough to turn by hand? How much should the clutch arm move up and down inside the clutch case? — Nick/via email

A: Adjusting the clutch on a Trident is one of those things that can take all day: Finding the sweet spot for three things at once can be difficult. You want the clutch to fully disengage when you pull in the lever, fully engage when you release the lever, and not load the bearing buried deep in the clutch basket when engaged. The original manual calls for the clutch nut to spin freely with 0.005in clearance, but the collective wisdom of Trident owners is that this is too much clearance. Setting it to the factory clearance usually results in difficulty finding neutral and creeping in gear with the clutch pulled in. The generally accepted method is to adjust until you have almost no clearance, then lock it with the locknut. If you can still turn the big nut by hand when the clutch is relaxed, you have it properly adjusted. Start by adjusting the cable so that the arm on the actuating mechanism inside the transmission outer cover is between 3 and 4 o’clock when the clutch lever is released. Make sure the arm isn’t touching the case stop. Tighten the pull rod through the big adjusting nut until it is just tight. Keeping the adjusting nut steady, loosen the pullrod about 30 degrees. Lock it down using the locknut without moving either the adjusting nut or the pullrod. It helps to have three hands for that part of the procedure. Try to rotate the big adjusting nut with your fingers. If you can then the clutch is adjusted properly. Any minor adjustments should now be possible from the adjustment screw at the clutch lever. MC


Tech Corner 

Honda oil pressure

Q: I have just finished rebuilding a 1970 Honda CB750K. It is my first attempt at rebuilding this type of engine. I have rebuilt other types with good success.

I now have about 480 miles on the engine and it is running great. It sounds good and doesn’t leak a drop. My problem is the oil pressure. Lately I find that after running the engine for about 30 minutes the oil pressure light comes on at an idle. I suspected the oil pressure switch. So I pulled it and have installed a pressure gauge. When cold the pressure starts at about 65lb. After running for about 15 minutes it drops to 60lb and remains there no matter how long I run it. — Daniel Pensyl/League City, Texas

A: According to the shop manual, the oil pressure bypass valve is set to 56.9psi at 4,000rpm for an engine temp of 176 degrees Fahrenheit. It looks like your engine has the correct oil pressure. An old rule of thumb was 10lb of pressure for every 1,000rpm, which makes your setup exactly right at about 6,000rpm. If your oil pressure light continues to light, it could be the switch that’s faulty. They’re still available for about $35. If you look for it on a parts schematic, it’s part no. 37240-P13-013 on the starter motor schematic. MC


Tech Corner 

Clutch issues

Q: I have a 1984 Honda Nighthawk 700 with a clutch problem. When I first started it after it had been sitting for three or four weeks, the clutch needed to be broken loose. Then it would work fine, but when stopped it wanted to creep. I rebuilt the master and slave cylinders. After this the pull felt better, but it did not fix the problem. With 30,000 miles on the clock I felt replacing the clutch would fix it, so I installed EBC plates and springs. I deburred the clutch basket and checked for smooth movement of the plates and steels, and all was fine. I still have to break it loose after the bike has been sitting for a long time, but now after riding for a while, if I stop to fill up, the clutch is locked up hard. It works fine if I do not turn it off. I spoke to EBC and they are sending me a new set of plates under warranty, but I would like your thoughts before I dive back into it. — Richard Porter/via email

A: Sticky clutch plates are a daily hazard on my old Triumph 500, usually cured by pulling in the clutch and kickstarting the bike. You might try that, but substitute electric start for the kickstart. How does it shift normally? Is it quiet or is there a clunk? I’m trying to figure out what would glue your plates together when the bike sits for a few minutes. I assume you’re using a good motorcycle-rated oil. Although failure to do so usually results in clutch chatter, did you soak the clutch plates in oil before you installed them? I’d love to hear from readers who have experienced this problem and how they fixed it. MC


Tech Corner 

The great oil question

Q: What type and brand of oil should I use in my 1992 Honda Nighthawk? It has 15,000 miles on it. Do I have to be concerned about using a certain kind of oil for a wet clutch? — Vaughn Giddens/Northeast Texas

A: Here’s a question with no answer that pleases everyone. Every brand of oil has its cheerleaders. The only thing I will say is that for a vintage bike with a wet clutch you should stay away from modern oils with friction modifiers. They will usually be identified as those oils with a very low winter (W) weight, i.e., 0w-40. The friction modifiers will make your clutch slip. Another topic for endless discussion is the amount of zinc dialkyldithiophosphate (ZDDP) added to the oil. This additive helps lubricate high pressure contact zones like flat tappets and camshafts. Unfortunately, phosphorus is poisonous to catalytic converters, so modern oil formulations contain less than oils formulated before catalytic converters came into widespread use. If you’re stuck using an oil with low ZDDP percentage you can always use an additive. Be careful though: Too much ZDDP is almost as bad as too little. MC


Tech Corner 

Oil-filled muffler

Q: While riding my 1971 Honda CL450 one day, a clattering noise came from the engine. When I returned home I left the bike idling in the driveway and soon discovered a pool of oil. One muffler was filled with oil and oil was dripping out through the bottom vent hole. What happened inside the engine that would cause this? - Wes Martin/via email

A: Unfortunately, any number of things could have gone wrong. Did the bike run any differently after you heard the clattering noise? Having one muffler fill with oil makes me wonder if an exhaust valve guide has come loose and is draining oil from the head directly into the exhaust. I’m afraid you’ll have to pull the top off the engine and do more research. MC


Tech Corner 

Sticking starter

Q: The starter won’t disengage on my Honda CB550. The instant you turn on the key, the starter motor starts to turn. What’s wrong? Is it my starter button? - Kurt Limesand/via email

A: It may be the switch in the handlebars, but there is also a strong possibility that you have a stuck starter solenoid. I’d start by disconnecting the thinner signal wires to the solenoid and turning the key on again. If the problem disappears, the starter button circuit is shorted out. If the problem persists, your starter solenoid is stuck and will need to be replaced. MC

The sound and the fury: celebrate the machines that changed the world!
First Name: *
Last Name: *
Address: *
City: *
State/Province: *
Zip/Postal Code:*
(* indicates a required item)
Canadian subs: 1 year, (includes postage & GST). Foreign subs: 1 year, . U.S. funds.
Canadian Subscribers - Click Here
Non US and Canadian Subscribers - Click Here

Motorcycle Classics is America's premier magazine for collectors and enthusiasts, dreamers and restorers, newcomers and life long motorheads who love the sound and the beauty of classic bikes. Every issue  delivers exciting and evocative articles and photographs of the most brilliant, unusual and popular motorcycles ever made!

Save Even More Money with our RALLY-RATE plan!

Pay now with a credit card and take advantage of our RALLY-RATE automatic renewal savings plan. You save an additional $4.95 and get 6 issues of Motorcycle Classics for only $24.95 (USA only).

Or, Bill Me Later and I'll pay just $29.95 for a one year subscription!