'78 GL Not Quite There Yet

[tomk1960]

After essentially finishing my '78 GL restoration, I'm experiencing issues with the way it runs. It starts and idles nicely, but under load or hard throttle, it stumbles, bogs down, and doesn't pull like it should. Something is holding it back. It's a 15K mile motor, so hopefully it's nothing major internally. Here are some facts to help narrow down possible cause:

Carbs professionally overhauled by a highly respected forum member.
Compression numbers are ok, but not thrilling. 140, 160, 145, 140.
(I may check compression again with all plugs removed at the same time)
Paper air filter
Points gaps in spec
Valves adjusted to .004
Static timing test looks ok, but I may repeat and try tweeking to see if it changes anything
Harley take-off mufflers installed
New belts installed

I know that numerous members here have used similar take-off mufflers without having to re-jet, so I hope that they aren't the issue.

Is it possible to run like this if the belts were off by a tooth?

Any suggestions or advice will be greatly appreciated, especially from anyone who may have experienced and remedied a similar issue.

Thanks!

[twowings]

If they are catalytic style mufflers, they may be too restrictive.

[chewy999]

I'm in a similar position with my 1980 1100. I'm happy to ride it but when I open the throttle it just doesn't sound or feel like it should. My carbs were built by a respected member too, but the carbs still have to be set to the bike and some parts like jets may be worn. My compression test figures were all in the 160+ range, so I assume the valves and heads are ok. Points back to carbs imho.

[tomk1960]

If they are catalytic style mufflers, they may be too restrictive.

Is it possible that even this style muffler could be catalytic?



I'll find out what year/model HD these came off of and can then confirm. If that's the issue, the fix is easy.

[OCR]

If they were catalytic style mufflers there will be a port for the connection back to the intake that needs to be plugged.

[Sugs]

If the cat is in the muffler you can take them off and look down the inlet. If you see honeycomb like material, that's the cat.

[desertrefugee]

Those look a lot like my non-cat Sportster mufflers. A quick way to eliminate the exhaust restriction question would be to pop them off and go for a "loud" ride. You'd know pretty quickly if that's the problem.

If not, I'd look for stuff like choke linkage sticking and keeping the blades closed or partially closed.

...Or maybe the advancer plate is gummed up and not free to move.

It'd also be pretty easy to pop off the timing covers, roll the engine to TDC (T1 mark) and see how things line up.

<EDIT: Of course, the assumption here is that the carbs are right. Sticky slides would exhibit the symptoms you describe, too>

[gltriker]

If the cat is in the muffler you can take them off and look down the inlet. If you see honeycomb like material, that's the cat.

H-D Softail slash-cut catalyst mufflers

DSC00577.JPG (97.17 KiB) Viewed 96 times

[tomk1960]

I found out that the newer HD mufflers have a steel plug pressed into the middle that creates a lot of restriction. Both of these mufflers had those plugs. On top of that, one of them is marked "catalytic" and had the honeycomb material on the header end. I was able to punch through that with a 1" iron pipe and knock out the both plugs.

I'm not sure if these can be considered equivalent mufflers in terms of flow, since there's still honeycomb material going in a few inches on one of them. (even though there's a 1" hole going through the center)

They're back on the bike, so I'll give it a short ride once the roads dry up. Riding without any mufflers is also a good idea if it still doesn't run right.

Thanks for the info and suggestions!