I'm having an issue with my 73 XLCH. It starts, idles and cruises fine, however, when I hit the throttle like to pass someone, it pukes out. If I roll on it slowly, it's fine.

It currently has a Keihin butterfly on it that I bought new from the dealer in '94 but I also have the original Bendix. Both carbs have been cleaned and rebuilt and it acts the same with either carb. I do have the FM that I used for the Bendix but the Keihin I counted turns and was careful not to disturb the float setting. I also did not have a diagram for the Keihin to ensure I got all of the passages.

I am by no means a carb tuner but I turn a pretty mean wrench. Is this just a jetting issue?

Thanks,
Dave

 

have you checked for intake leaks? what about valve setting? sure sounds like a accelerater pump problem

 

I have not checked for intake leaks but I did set the valves last fall. The accelerator pump is new but these days, that doesn't mean anything.

 

Does the accel pump squirt fuel into the throat of the carb when you twist the throttle?

 

could have a blockage in a passage for the accelerator pump, is it adjustable?

 

Does "pukes out" mean it sputters?, or do you mean that it bogs down? Sputtering is a lean condition and bogging is a rich condition. Sputtering on acceleration like you describe can be the fuel level in the bowl is too low.

Since this is occuring at full throttle operation, if it is a jetting problem, it is with the main jet.

What main and slow jets are in the carb? How many turns out on the pilot screw?

To determine the year of the Keihin we need to know if it is fitted with a single throttle cable [1980 and previous] or for dual throttle cables [1981-on]. Does it have the evaporative port [82-on] and/or a VOES port [84-on]? Is there a tag on the top of the carb with a part number?

Is it a 38mm carb intended for a big twin? or a 34mm Sportster carb? Measure using two pieces of cereal/kleenex box cardboard one 34mm wide the other 38mm. Check to see which better fits the most narrow part of the venturi.

Knowing these we can know what were the stock jets for the carb.

Are you running free flow intake and exhaust? or not? This will help also in determining if the current jets in the carb are adequate.

 

Thanks all for the ideas. Some unforeseen issues pooped up over teh weekend so the bike has to wait for a bit. I will get back you you all soon.

IronMick, I'm going to go with sputtering. It will make a slight 'cough' and then act like it stalled. If I let off the throttle and just roll into it slowly, it will accelerate just fine.

I will get you all of the carb info as soon as I can.

Dave

 

Ok IronMick, here's what I have so far:

What main and slow jets are in the carb? How many turns out on the pilot screw? Not sure yet. I haven't had a chance to take it apart to look. It does have a big brass tumb screw on the top. I thought this was an adjustable main kit that I installed many years ago but could be wrong. Like I said, carbs are pretty foreign to me.

To determine the year of the Keihin we need to know if it is fitted with a single throttle cable [1980 and previous] or for dual throttle cables [1981-on]. Dual cables but I have it set up to use one so I could stay with the original 73 throttle setup on the handlebars.
Does it have the evaporative port [82-on] and/or a VOES port [84-on]? Not sure. It has an angled port that sticks out just in front of the thumb screw mentioned above. It is plugged off.

Is there a tag on the top of the carb with a part number?
Two tags: 27 469-83 and -0365.

Is it a 38mm carb intended for a big twin? or a 34mm Sportster carb? Measure using two pieces of cereal/kleenex box cardboard one 34mm wide the other 38mm. Check to see which better fits the most narrow part of the venturi. 34mm

Knowing these we can know what were the stock jets for the carb.

Are you running free flow intake and exhaust? or not? This will help also in determining if the current jets in the carb are adequate. S&S Super air cleaner with K&N filter. Stock intake manifold. Drag pipes with 4 inch long baffles.

I will try to get jet sizes in by the weekend.

Dave

 

Blackcherry Low - Yes it does squirt.

 

With the choke plate open the squirt of fuel should go thru the semi-circle cutout in the choke plate. It should be aimed just to the left of the center of the back of the carb. If it is aimed at or to the right of center most [or all] of the fuel will go to the front cylinder. Let me know if it needs to be re-aimed.

The capped angled port is the evaporative port. With no VOES port it is a 1983 Keihin butterfly carb. There should be one "tower" passage on the top of the carb, centered side to side, at the back. This is for the pilot screw. Probably that is where the brass thumb screw is, so it is not an adjustable main.

Stock jets for 1983 are #160 main and #52 slow. With the K&N intake and the baffled drag pipes you probably need about a 170 main and a 58 slow. But there is a proper way to determine that. I'll go thru it when we know for sure what is in there.

27469-83C is the correct part number for the 1983-85 carb.