BLOOD BROTHERS

I BELIEVE my Japanese import Suzuki 750 Katana is restricted in power.
How can I de-restrict it? It revs out but there's no real power at six to seven thousand rpm.
What would be the best aftermarket exhaust to fit and should I run on leaded petrol?
Nick Macken, Diss.

This is a new one on me. Some Jap imports have a restrictor attached to the speedo, some have rev limiters and ignition mapping that hold the engine back. There are several import specialists that might have the info to hand - unfortunately I do not for this model. The equivalent UK/Euro model exhaust should fit straight on so find a friendly dealer or manufacturer with a stock system and nip down to try it before you buy. CP


Mixed and matched

MY 1977 Suzuki GS550 has a top section from the 650 engine. The carburettors are from the 550 and I find it very hard to get the timing right. When I run it the plugs get very black. The clutch is also very heavy even though I have changed the cable and clutch springs. Why is it so heavy?
Daniel O'Connell, Limerick.

You have a strange mix of engine parts indeed. The ignition timing for a 550 is clearly marked on the advance/retard unit situated on the right hand end of the crankshaft.
The blackness of the plugs can be many things, from worn rings and valve guides to the different carburation and exhaust system requirements of the 650 engine. You can check the compressions to determine the condition of the top end. If all is well the mixtures will need setting up.
The clutch stiffness could be down to several factors. If the cable is new and well lubricated then start at the 'worm' housed within the cover just above the gear lever. This worm screw pushes a rod through the gearbox lay shaft to the clutch outer. If this rod is bent or worn, it could be another cause of friction. CP


Honda choker

THANKS for your previous help on my Honda CB77. I've since got a 1995 Helix CN250S which has been used for courier work and covered 35,000 miles in two years (52,000 now on the clock) so it will need some work doing. The carb has an automatic choke and the handbook says to let the temperature needle go up two marks before riding away. However, the bike stops at road junctions and also after a couple of minutes on tickover. Would you say that auto-choke is shot?

A problem with an automatic choke is that it will stay on until the engine reaches its normal running temperature and makes the engine run on the rich side for the first ten miles or so.
All that I can suggest is that you give the bike a thorough service replacing all the filters and spark plug. With over 50,000 miles on the clock I would not expect the engine to be as good as new but it should travel for a lot further yet. At this mileage I would not expect that the auto choke is shot.
The only manual that Honda now list for your machine is part number 68KS400V priced at £8.64 plus VAT. DB


Honda under load

MY daughter has recently passed on to me her 1990 Honda H100S-J (I know that's a bit new for Mechanics). The problem is it will not pull away with less than 4500 revs. I know I'm not light at 15 stone - my daughter is less than nine stone.
Is this usual or do we have a sick bike? It starts and revs freely but will not pull unless revving well. All of my two stroke experience was on Bantams and Ariel Arrows so this is a little new to me. I also own a 1963 G80 Matchless and a 1976 GT250A Suzuki which is being rebuilt.
Stewart Freeman, Northampton.

Well, don't tell anyone but my first motorcycle was an Ariel Leader in the middle of the last century followed by a Ariel Sports Arrow (glutton for punishment) so you and I have some good memories of two strokes.
However, I did learn the error of my ways and purchased my first Honda - a CB77 - in 1966 and have been a Honda man since then.
As you say the engine will rev freely until under load I would expect that your classic two stroke problem is a blocking exhaust. The Bantams and Arrows suffered the same problem. Also remember that this machine is only 100cc so it will need to rev to give any performance. DB