Need help with low speed surging

[Ndulucky13]

Ok so far i have cleaned the carbs made sure the dots are lined up on the slides. Tried to set the timing perfect but think I'm failing at it. Bike is a 72 gt550 was ridden by previous owner 2k miles then sold to me. He was not mechanically minded, front brake shoe cams where almost locked up and insanely touchy and he thought it was supposed to be that way. I cleaned them and reassembled and now it works perfect. The problem is that under 1/4 or less throttle it surges and upon letting the bike coast in gear it surges. Anything over 1/4 throttle it runs like a stabbed rat. I've had 54 bikes and counting now including quite a few 2 strokes and have not felt this surgy problem before.

[GTandcbr]

Firstly have you cleaned the pilot jets with carb cleaner and compressed air? Also you need to check the small pilot jet outlet ,which can hardly be seen, engine side. All of these need to be clean. It goes without saying that the air filter is clean and carb rubbers are tight and leak free?. Here is the carb manual to help. Good luck
http://www.3cyl.com/mraxl/gt/manuals/su ... /cover.htm" onclick="window.open(this.href);return false;

[Ndulucky13]

Yep cleaned both passages with air compressor and cleaner carb boots are new as is air filter. No leaks according to a spray test carbs are set at idle screws 3.5 turns out idle awesome at 1100 rpm. I have 2 questions is there an idiots guide to timing these things? I have a test light and a dial indicator for setting the piston btdc. 2nd is there a fix for increasing pilot jet size? I had read about that.

[Ndulucky13]

I have the 72 carbs they are way different then those

[GTandcbr]

If your airscrews are 3.5 turns out there is the problem. According to the manual you should start at 1 1\4 turns out. Airscrew will stop having any effect at all at 3 turns out. I have fitted one size bigger pilot jets (30) to cure a fueling issue(pinging) the carb manual link refers t the later gang carbs but are basically the same.if your bike needs the airscrews 3.5 turns out I would suggest you need smaller pilot jets not bigger.

[Ndulucky13]

My individual idle stop screws are a 3.5 turns out my air screws are at 1.25 turns

[GTandcbr]

OK confusion over screws! Personally I found by turning the airscrews in 1\4 of a turn it improved the running of the bike. The cause of the surging I think is when you come off the throttle the motor runs lean. Turning the airscrew in makes the mixture richer. The rule of thumb is if you need to turn the airscrew in so it is less than 3\4 turn out you need the next size up pilot jet. As I said I have done this and it improved everything. There is no doubt they had problems getting the fuelling right on these early 550's

[GTandcbr]

With regards to the timing I have electronic ignition and set it up with a strobe but I'm sure someone will be along to help shortly.
Another link for you
http://www.3cyl.com/mraxl/gt/manuals/gt ... 550-40.htm" onclick="window.open(this.href);return false;

[Ndulucky13]

I will have to try that tonight. Thanks for the input on that. What about timing though? Anyone have a video of it being done?

Where did you get you ignition?

[GTandcbr]

Can't find a 550 video but this is a 250 hustler twin.same principle
https://youtu.be/-a1GEY_W5Og" onclick="window.open(this.href);return false;

[Ndulucky13]

Thanks for the video of the install of the electric ignition. I really just need a points timing video right now I have been looking but I can't find one that is super clear.
I tried setting points gap then going back and adjusting the left cylinder points to open on the timing mark but no matter how much I turn the plate it stays on (the Test light) telling me that the points are not closing when the should so I can set the moment they begin to open with the timing mark

[GTandcbr]

https://youtu.be/yjvc4912wA8" onclick="window.open(this.href);return false;

Explains it well I think.

[Ndulucky13]

That is perfect thank you very much for finding one that makes sense ha

[Vintageman]

The problem is that under 1/4 or less throttle it surges and upon letting the bike coast in gear it surges.

To me this is Needle Jet (NJ) circuit. At 1/4 throttle the NJ needle metering barrel (the first 1/4 inch or so inside) needs to be precise: smooth and shinny. Have to take it out and look into barrel at needle inlet with very good light and good eyes or help of low power magnifying glass. if pitted it causes turbulence to fuel flow and poor atomization of fuel with air.

[Vintageman]

The problem is that under 1/4 or less throttle it surges and upon letting the bike coast in gear it surges.

To me this is Needle Jet (NJ) circuit. At 1/16 - 1/4 throttle the NJ needle metering barrel (the first 1/4 inch or so inside) needs to be precise: smooth and shinny. Have to take it out and look into barrel at needle inlet with very good light and good eyes or help of low power magnifying glass. If pitted it causes turbulence to fuel flow and poor atomization of fuel with air.

If you 100% close throttle, does it still surge?

Inspect NJ if your problem remains