Everything may be just fine but I needed to ask. I have been following several threads here and in another forum regarding exhaust pipe changes and re-jetting of the carb to accommodate the change. I removed the original factory exhaust pipes off my '73 and replaced with pipes from a company called Santee. The label says its their "Dyno Powered Exhaust System" tapered style and for my year and model. Looking into the pipes from the back end and there are baffles of some kind. As these are providing some back pressure can I assume the original Bendix carb and jets are o.k.? Is there any sort of 'check' I can do to see if an adjustment (assume main jet size) is required? Seems to run (at this time) fine, but just wanted to be sure. Thanks for all the good info you guys provide it is appreciated....

 

The only test is to ride it to see how it performs and check the plugs. Remember it usually takes at least 25 miles for new plugs to give an accurate coloration.

 

It is most unlikely that you would have to change the main jet. You may have to richen the idle mixture a little, or possibly change the slow jet. Follow this pilot screw setting pocedure ...

Setting The Pilot Screw on Your IronHead

If the carb is old and dirty the pilot screw passage may be gummed up such that you will not be able to "gently seat" the pilot screw reliably. If this is the case remove the carb from the bike and clean it up. Some guys try to do carb work with the carb in the bike. IMO this is a very bad idea.

In the pilot screw passage there should be, in this sequence: screw, spring, washer, o-ring. [Often POs have installed these parts in the wrong sequence; remember that the purpose of the washer is to protect the o-ring from being damaged by the spring]. The screw usually comes out easily. The other parts may require some work. The best technique is to stick a pipe cleaner in the hole, twist it around, and, like magic, out come the other parts on the end of the pipe cleaner.

EDIT: The above info on the pilot screw applies to 1979 and newer carbs. For 77 and older there is nothing in the passage except the screw itself.

1. You need to have easy access to the pilot screw, easy enough to reliably judge "screw it in until gently seated". Loosen the front fuel tank mount bolt; remove the rear fuel tank mount bolt; prop the rear of the fuel tank up on a piece of 2X4; on some bikes this will not be necessary.

2. With the engine cold [so you do not burn your fingers] turn the pilot screw in clockwise until it is gently seated. Count the number of 1/4 turns as you do it; write the number down. Back it out to the original setting. You may need to return reliably to this setting after experimenting.

The "normal" starting point for this process is 1,1/4 [according to the 79 - 85 FM] or 1,1/2 [according to usual practice] turns out.

EDIT: An old HotXL magazine article recommends for Keihin butterfly carbs between 1/4 and 1,1/4 turns out. My experience is that this works best. If you are more than 1,1/4 turns out your pilot jet is too small.

3. The engine must be at full warm up. It will have very hot parts; to avoid burned fingers have a well lighted, comfy place to work.

4. Set the engine idling at about 1000 RPM. You want it to be idling at the slowest speed that is consistent with a smooth idle so that you can hear or feel slight changes.

5. Turn the pilot screw in clockwise until the engine idle becomes worse; tending to stall. Count the number of 1/4 turns as you do this. Then turn the pilot screw out counter clockwise until the engine idle gets good, then becomes worse, tending to stall. Count the number of 1/4 turns as you do this.

6. The best setting for your bike will be somewhere between these two settings. The FM says to use the leanest setting [most screwed in] consistent with a good idle quality. Some guys say to go between the two settings.

It should be between 1/2 and 1,1/2 turns out from gently seated. If it is not within this range you should change the slow jet.

EDIT: I follow the advice from the old HotXL mag article - set it between 1/2 and 1,1/4 turns out.

7. You may have to adjust the idle speed.

8. Make sure that the spark plugs are clean, then ride the bike around your neighborhood for 10 minutes. Keep it under about 15 MPH so that you are on the "idle port", not the "idle transfer ports", the "mid range port", or the "main jet" [see carb diagrams in FM]. Hopefully the plugs will come out a nice medium gray or tan color. If they are too dark you can screw it in another 1/4 turn; too light screw it out 1/4 turn, and try the ride again.

9. If they are really light or really dark the problem is not with the pilot screw setting. For example, too light might mean an intake or exhaust leak, and too dark might mean the pilot jet is too large [among other possibilities].

10. My experience with this process is that after making a change i have to clean the plugs and go for a good ride [say, a half hour or more] before i can trust that the new results are reliable.

 

Like 47Harley said, all you can do is run it a bit and see if the power band was affected.
You can look at the plugs but with today's no lead gas it is not like taking plug readings in the old days of leaded fuel.
My guess is that everything is going to be the same. Where I have found great differences is going to a 2 inch set of pipes or maybe a 2 into 1 where the end pipe is a large 4 inch diameter with no baffle. That kind of thing makes a huge difference and not for the good either. All low end power is lost. Top end runs fine but it takes you a day and a half to get there.
pg

 

Plug coloration in these days doesn't mean a whole lot but still needs to be looked at. Just put you *** in the saddle and see how she runs.