alfa75uk

Member
May 8, 2007
2
0
Hi I'm new to this site so please bear with me...

I have a '79 IT400 which is in excellent condition. I'm very pleased with the bike but it does run rich and there's spooge on the back mudguard.

So here's what I know. Carb is a standard VM38SS. Jetting is standard 370 main, 60 pilot. Needle jet and needle jet are standard Q-0 and 6F16. Float height is correct. Premix is Maxima Super-M at a ratio of 32:1 on 92 Octane pump gas. Plug is a standard B8ES. The previous owner has dropped the needle jet as low as it goes and the mixture screw is 2 1/4 turns out.

The bike starts great, first time every time. It won't rev out until you hold the throttle wide open and drive through a "stuttery" part of the rev range. Once you've done this it will run fine as long as you keep riding it hard but if you ride slowly it will bog down again. I've done a plug chop at wide open throttle and the plug is black.

The bike will idle but if left it will cut out and again the plug is black.

So it appears that it is running rich from idle to full throttle. I have cleaned the carb and also checked that the choke is operating correctly. Should I just try leaning it out on the jets or could there be something else going on? Oh and elevation here is just above 2000 feet if that makes a difference. Thanks for any help you can offer and apologies for the length of thie message! :nod:
 

jsantapau

Member
Nov 10, 2008
340
0
it is possible that the little clip that holds the throttle cable on to the slide is on wrong blocking the bleed hole in the slide, Unscrew the top of the carb ,pull back the spring off the slide and hold the slide upside down, and the clip I am talking about should slide right up/(down ) the cable , look down inside the top of the slide and you will see a small hole, make sure that the clip when installed is not covering the hole.
 

alfa75uk

Member
May 8, 2007
2
0
Hey Okkarner, my solution was to remove the baffle from the muffler and repack with new material as the original packing material was completely saturated/blocked with oil. I initially tried leaning out the mixture through smaller main jets which was a bad idea (but seemed like a good idea at the time...) Aside from that these bikes like to be ridden hard! Good luck.
 

okkarner

Member
Oct 7, 2010
11
0
The packing didnt help me. I ran a 300 main jet and 40 pilot with the air screw 2 turns out. Runs like a beast and the plug is a nice light brown.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
That bike came from the factory jetted for a premix ratio of 32:1? A plug chop on an old plug is futile, a few seconds on a new plug will do. The stutter before clearing out sounds normal anyways! Step 1, replace the float valve and seat if applicable. As long as the rest of the carb is not worn past service. Then read:http://www.dirtrider.net/forums3/search.php?searchid=1089255&pp=20&page=1 . At least a few thousand have asked basically the same question as you. Vintage Bob
 

okkarner

Member
Oct 7, 2010
11
0
Factory settings are 380 main 60 pilot running 20:1. I tried this and it ran about the same maybe a little worse but there was alot of spluge on the rear wheel (my bike is a IT400 turned into a cafe bike so the pipe runs under the motor)
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
okkarner said:
Factory settings are 380 main 60 pilot running 20:1. I tried this and it ran about the same maybe a little worse but there was alot of spluge on the rear wheel (my bike is a IT400 turned into a cafe bike so the pipe runs under the motor)
Where did the down swept pipe come from?
 

okkarner

Member
Oct 7, 2010
11
0
Im not sure. It was on the bike when I bought it. Someone had started the transformation but it went terribly wrong and looked silly. I modified the frame and built the tail section. Put a different tank on it, finshed the details, and it came out looking like this:
 

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