Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Q: I have a 1973 Hodaka Wombat that is all stock and in nice shape. It starts right up and runs well up to around 35mph, when it bogs down and won’t go any faster. I was told by a mechanic that the 125 should go to 50mph no problem. Is this normal for stock gearing, or might I have a clogged main jet or some electrical problem? I use premix 36:1. It has a working speedometer and lights. What is a realistic top speed for this bike and how can I get more top end? — Bill Baillie/Rhode Island
A: Two-stroke engines are very dependent on their exhaust for efficient running, so I’d probably start there. Make sure the baffles are in place and not clogged with carbon and oil. The next step I’d take would be to pull the carburetor and compare the jet sizes against the stock requirements. For a 1973 Wombat with a Mikuni VM24 SH-83A carburetor, the main jet should be a 180, the needle should be a 4J1 and the needle jet should be a 0-4. If you have a VM24 SH-83B carburetor, the numbers are 160, 4E1 and N-8. The needle clip should be in the third groove from the top for both and the float height should be set at 22.5mm for both. My Clymer manual calls for a 20:1 fuel-to-oil ratio.
How does it fail at the top end? Does it stumble and cough, or just die out? I spoke to my local Hodaka expert (who has a basement full of restored Hodakas), and he thinks you may be starving for fuel. First try raising the needle by lowering the needle clip one notch and see if you have any improvement, however minor. If you do you will know you are on the right track. You may be able to fix it by raising the needle, or it may take a larger main jet. You’ll have to experiment to see what works best. MC