'57 Huntmaster - Engine running problems

[roger.attwood]

Hello again. I'm after more advice, this time on how to get the engine running properly.
When I bought the bike it came complete, unused for 12-odd years, stored in a garage. I've stripped it (as some of you might remember from previous posts), re-assembled it, and run it for about 40 miles. During the rebuild I replaced one inlet valve guide.

When I first timed the engine, I did it during the rebuild, so I had access to the timing marks, and the piston (head not fitted). Timing a bike of this age, with a magneto, was new to me, but I think I got it right. Measuring 11/32" BTDC wasn't easy - even with reading glasses! I did remember to jam the A/R mechanism to full advance. The bike started OK - a little bit of fettling the slow running and the idle mixture screw. However, I couldn't get more than 60 mph out of it, the plugs were always sooty, and I had the feeling it was running hot. All the carb jets, needle settings etc are by-the -book. I lowered the needle by one groove, but no real change. Perhaps because doing the timing seemed so difficult, almost hit-and-miss, I had it in my head that the timing was too advanced, and couldn't advance further to allow for a higher speed. So first question - can a too rich a mixture at full throttle stop the bike from reaching a faster speed than 60 mph? Second question - if the timing is too advanced, can it also give the same problem?

I had some problems with the rear wheel, so while the bike was off the road I had another go at timing. This time I had to use the 'feel the piston down the plughole' method, to get TDC, which I have used before successfully on my BSA C15. Again, measuring 11/32" was not easy. The bike started OK again, but this time it wouldn't run if I closed the choke, and it was spitting back through the carb (blue flames). Thinking it was too weak, I raised the needle again to the middle (3rd) groove. Still no difference - it needs full choke to run, but if I open it up with full choke it accelerates, but then runs ragged and dies away. It seems that the mixture is too weak, so I'll check the carb for blockages.

How much does the timing have to be out to make a difference. The method used to do the timing seems so hit-and-miss (no strobe, no timing marks, no timing disc).

Meanwhile, I'm going to strip the carb, and check out the jets, drilling etc. I know the float level is spot on (I followed the Youtube video, to check the fuel surface is level with the dot on the chamber cover).

Any help much appreciated. I can probably get a professional to sort it, but there's always that bit of pride in doing it yourself.

[johnwalsh]

The timing has to be right, being a little out can make a big difference. Blacking plugs and lack of power sounds more like too retarded than advanced. When setting the timing the best method is to gauge when the piston is at TDC ( both valves closed) by use of a piece of wire ( spoke) long enough or bent so as not to get lost down the plug hole. Mark the spoke with a relevant place on the head with a hacksaw. Then remove spoke and make another cut 11/32" higher. Insert spoke and turn the engine back using the rear wheel with engine in gear so the top mark is adjacent to the same place on the head. If you choose to use the right hand cylinder then you need the mag points somewhere near the 7 o'clock position ( from memory). This ensures that the cam is acting on the points relevant to the r/h cylinder. I use a fag paper in the points to judge when they are just starting to open. Make sure you don't leave any fag paper behind, its been done I know.Check the timing after the mag pinion has been tightened. I wouldn't advise messing about with the carb until you sort the timing, one thing at a time.

[joegibbs]

Just a small point. I always turn the engine backwards past the relevant timing point as measured on either a degree wheel, or by piston hight. Then bring the engine forward to the desired timing mark by turning the engine in it's usual working direction. This removes any errors caused by drive backlash between the engine and mag./distributor.

[paul.jameson]

Having set the timing - check it. Do this, as Joe advises, by turning the engine forward with the back wheel so that you remove the errors caused by backlash. See when you can just feel the fag paper start to slide and check the distance down the cylinder. You may well find it is wrong, in which case, have another go, then check again. If the second time you check it is wrong by the same amount as it was the first time, adjust your settings as you time the engine to compensate. Then check again, and so on. You are likely to need some patience but believe me, it can be done.

[Steven.Carter]

Hi Rodger.
It's not too difficult to set the timing with a strobe. You do though have to remover the primary outer chain case and then refit the clutch. Timing can then be done from the engine shock absorber. This way has the advantage of checking the auto advance is working properly.
Sorry Rodger but I can't remember whereabouts you live but if I'm ever pasing by I'd gladly have a look.

Steve

[roger.attwood]

Thanks for all the advice. I had another go at the timing today - it took 5 hours, but I got it in the end!

On checking the timing from the last time, I found It was firing just before TDC. I repeated adjusting the timing several times and found it was consistently retarded. This agrees with your assessment John. In the end I fitted a 4BA ring spanner on to the nut in the middle of the points, and used it like a hand on a clock against the rim of the points recess. By marking off each attempt I narrowed down the position of the points until I had them opening at the right time. I found that roughly 1/16th on the rim equated to 1/32nd vertical movement of the piston.

I put everything together again and the bike started no problem (full choke). But when I eased off the choke and opened the throttle the engine coughed and died, with a bit of spitting back through the carb. In fact, the engine would only run properly with full choke. Obviously a very weak mixture - too much air or not enough fuel. I know there are no air leaks on the carb-to-engine joint, and as I had taken off the carb and checked it (see top post) I was sure there was nothing wrong there. So not enough fuel, but all the jets were clean. But it had to be the carb, so I took it off again for a look. As I up-ended the carb to drain the fuel, the needle fell out - I hadn't noticed it wasn't still attached to the slide when I undid the top knurled ring. I thought the loose needle was strange because I was sure I had engaged it in the clip securely. However, when I pulled the clip out it fell apart. I quick trip to Burlen Fuel Systems in Salisbury (15 minutes away) for a new one.

Now the engine is running OK except for the odd pop back through the carb as I open the throttle. I'll check the needle setting as I found it difficult to judge if the clip was in the correct groove. I'll raise the needle one groove and try again. Anyway - I think I've cracked the timing at last!!

[paul.jameson]

I am glad you timed it correctly in the end. Next time, it will be a lot quicker than 5 hours - which is good, because next time it might be at the roadside when you are many miles from home, enjoying riding the machine. And you will be able to continue enjoying riding the machine - because you have now mastered it and can set it up as you need to - anywhere.

[Steven.Carter]

Well done Rodger. When your in the midst of trouble it doesn't seem you'll ever get it going but the sense of accomplishment when it's going great is priceless.

Steve

[roger.attwood]

After managing to set the timing correctly, I still only get 60-65 mph out of the bike. I've been adjusting the timing by opening the points gap (advancing), and I'm getting 65-nearly 70 mph with the gap at 18 thou. Once I'm happy I can measure the piston BTDC to get a figure that's good for the bike, and reset the points gap to 13 thou. What is the accepted top speed for this bike?

[Steven.Carter]

The fastest I've ever been on my Huntmaster was 80mph. Probably a genuine one though as it was taken by my sat nav.
I'm usually only doing just over 60mph most of the time and sometimes a bit more to get out of trouble. I've gone the electronic ignition route which has proved reasonably reliable when I've learnt how to join wires up properly