XR400 Carb issue
Posted 06 June 2012 - 10:19 PM
I am helping a mate sort out his 98 Honda XR400R. Bike runs fine, but we can onlyopen the tap slighty. When opened completely it floods. There is a sticker on the carb with an american flag stating "This Carb is for racing purposes only"
Is this the standard carb? Can anyone tell me what the standard jets are? or which ones we should use. The bike is stock standard, Standard pipe and air filter.
Posted 07 June 2012 - 06:23 AM
Post up a picture if you can.
Posted 07 June 2012 - 10:15 AM
What are you calling "the tap"? The fuel tank petcock?
Posted 07 June 2012 - 10:35 PM
Thanks so Far
Posted 08 June 2012 - 07:01 AM
Posted 08 June 2012 - 08:53 AM
But, it sounds like it could be an Edelbrock.
I have a scanned copy of the "Edelbrock Tuning Manual" in a "Word" format.
PM your email address and I will send same to you.
I would guess that the problem has to do with the float valve............missing, faulty, misadjusted.
I do not if the float valve on these carbs have a rubber piece like the stock carb, but I have an unused Edelbrock in my parts stash that I could open up to see?
Quote from manual:
"Edelbrock Pumper Series carburetors contain a small brass check needle that can fall out when the bowl is turned upside down"
Posted 08 June 2012 - 08:53 AM
Posted 09 June 2012 - 11:00 PM
I was mistaken, there is no american flag on the carburettor, There is a flag on the air filter ( I was posting when I was at work)
I can't seem to upload the pictures but here is some more information.
On the top it stats CR Flat, On the left hand side of the carb it states Keihin. Then there is a sticker stating "MOTORCYCLE RACE USE ONLY - KEIHIN". There is also a number S.10A3 LH.
Posted 10 June 2012 - 06:49 AM
Posted 10 June 2012 - 05:41 PM
This is a Keihin 39mm Slant body pumper... very rare.
Edited by Perc82, 10 June 2012 - 05:42 PM.
Posted 11 June 2012 - 10:31 PM
Posted 12 June 2012 - 06:31 PM
Posted 15 June 2012 - 07:57 AM
I have an issue with the throttle as well. Symptom seems to be the same. It starts fine, runs fine at low revs, but if you constantly turn more the throttle it starts to miss/ backfire. Then I tap the throttle fwd/ bck 3 times and runs as a beast. I am having some help from a friend, we are suspecting that the bike was jetted for cold temperatures since it was in centre UK and now it is in Malta, hence it is now in a hotter and more humid condition.
We are starting from the main jet as the issue seems to be related to the intermediate stage of the carb.
I just removed my main Keihin main fuel jet and I have a no of 178, which I am suspecting it to be too high!
I saw here a matrix jetting table comparing mikuni, keihin and OEM, if anyone has a link please post it as I am looking for it.
Posted 18 June 2012 - 10:38 PM
I have some main jets ordered, If I do not succeed I will dismantle the carb carefully and inspect the diaphragm for the pump.
Hopefully I will let you know the root cause.
Posted 21 June 2012 - 06:05 AM
While waiting for the parts I have dismantled my Flat CR and found the below;
- Oxidisation on the back part of the diaphragm (many thanks to your valuable suggestion)
- Contamination from the diaphragm in some areas of the carb.
- Needle circlip too loose in the slot. Needle position might have changed due to this clip being too loose.
My next step is a good clean up, and to look for info re float height adjustment.
Posted 20 July 2012 - 03:37 AM
Type; FCR 35 - 41mm
Main jet from; 178 to 162
Needle (OC) clip position from; 7 to 4
I am very happy with the outcome, but now I need to fine tune the slow cicuit as the bike is idling too fast in my opinion especially when it is heated up. Also according to the manuals I have read an ideal fuel screw set up is 1 to 2 turns out from slightly bottomed. Mine is only 1/4 turn out. This means that the slow jet is too rich. I have a 52 slow jet and bought 40, 42 and 45.
Till now I have installed 42 and had no positive results. I will install 40 and check it out. Luckily I replaced the original fuel screw with an extended T-handle so less hassle there to fine tune it during the process.
Will let you know the final settings when the bike is ideal.
If someone is reading, I need some clarification on the slow air jet please. My question is; where is the point to know that you need to change the air screw setting (adjustable air screw type) instead of further slow fuel jet & air screw adjustments?
Posted 20 July 2012 - 08:29 AM
Posted 23 July 2012 - 11:26 AM
I have checked the fuel screw and it is assembled according to the FCR exploded view.
I tried to look for the excel sheet for the ideal jetting according to temperature and altitude posted here by some members, but unfortunately I did not find it.
We have 35 to 38 deg celsius here in Malta, humidity is around 70% and altitude is low mostly near sea level. I think that the slow fuel jet is still big than it should be. With the fuel screw fully in the cyclinder is still firing. Luckily I had an adjustable slow air jet and found info on settings re turns out with respect to slow fuel jet sizes.
With a 40 slow fuel jet, 70 slow air jet and fuel screw 1/4 turn out the bike is still idling fast. That is why I would like some jetting guide for the slow circuit.