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DR650 FCR Carb Installed and Leaking

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Cross posting here for a broader audience. I'm searching here an elsewhere and reading old posts, but any advice would be appreciated. Carb in question is a Keihin FCR MX 39mm from a YFZ450, currently installed on a DR650 with all of Robs mods done by Rob for the PO.

First post last night...

So I bought an FCR from the Buy-and-Sell a couple of months ago from 28marcb and finally got all the pieces and parts together to do the install. Had the shock off for a rebuild by Cogent and took the opportunity this week to cut my airbox, and install the FCR and DG pipe while I had the tank, airbox, etc. off the bike. Everything went pretty well, following Rob's instructions and got everything back together about dusk tonight. Petcock on prime, couple of pumps of the throttle, open the choke and it fired right up. Played around a bit with choke/no choke, throttle pumps, and partial throttle to get it running and keep it running and adjusted the idle up just a bit and it's sounding NICE! (OK a little LOUD, with the DG pipe, but I have a GSX-R750 can to go on when I get tired of playing hooligan with the DG on.

First thing I noticed was a little whine/whistle and I wondered if I had an air leak, but I vaguely remember something about an FCR "turbo" sound, so I figure I'll do some reading tonight and verify.

The I noticed a little gas leaking from the bottom of the carb. I shut it down and grap a couple of shop towels and wipe it up. Still leaking, seems to be coming from around the area where the bowl joins the carb body. Touched the air screw and found gas there, but may just have ran there from somewhere else. I pulled the gas line to verify that the vacuum petcock was functioning correctly and it was.

Wondered if the PO may have had the bowl off before I got it and didn't tighten the screws, but a quick check with the allen wrench and they are as tight as I would have tightened them in the aluminum body.

I changed towels a couple of times and it appears that once the bowl emptied I'm not getting any more fuel.

So I'm reading and thinking and trying to plan my troubleshooting for tomorrow. I was REALLY hoping it would be ready for a ride Friday, so I'm going to get back on it early tomorrow afternoon and see what I can find.

I didn't check the drain plug (and may have not even had a hose installed on it) so maybe that's where the fuel was coming from, even though it appeared as though it was leaking around the front (lower) edge of the bowl/carb body seam? Is there anywhere else that I need to look for the leak?

I saw the post (and others) about the float level and seals, and I'll see if I can narrow it down and find the issue tomorrow. Here are my plans so far, and I would love any other advice you may have!

First I'll try the trick Rob has suggested to another member of opening the drain and then after the bowl is empty opening the petcock (prime position) to flow some fuel through the bowl and try and wash out any debris.

If that doesn't work, I'm going to see if I can turn the carb enough to remove the bowl without removing the carb from the boots/bike. Maybe I can get enough access to check the float seal is functioning correctly? Not sure if I can check the float level in this position, but may not need to?

While the bowl is off I guess I could also spray some carb cleaner around in there, but I hate to make a mess, so I may go ahead and remove the carb and do it right. Also, I'm not sure if the carb cleaner would be safe for all the parts exposed with the bowl off. I believe you're not supposed to get carb cleaner on rubber parts?

May need to replace the needle or some other parts due to sitting up several months? according to some posts. Based on where it appears to be leaking I guess it could be the gasket/o ring on the float bowl?

Your wisdom and advice are GREATLY appreciated!

James <><

P.S. I'm also looking for pictures and/or diagrams showing how all the hoses should be installed and routed to make sure that's all OK.

Second post tonight after another R&R and still leaking...

I decided to just go ahead and take the carb off. It's not much trouble and would give me better access to asses the problem. Carb off and checked the float and it seemed to be OK. Blow in the fuel pipe with carb upside down and tight as can be. Checked that the dran was tight and it was good. At first I thought there could be an issue since I could blow in the drain hose with the drain cut off, but I'm pretty sure I read that the drain is ALSO the overflow? Removed the bowl to inspect things and the float still looks good. I didn't check the level since the gas is definately NOT coming out the overflow, but blowing while raising the float definately shuts off the fuel. Since my leak is NOT out the overflow I'm going to assume the float is still set correctly as delivered to Marc by Rob. Found that blowing in the drain hose with the drain closed air comes out a brass tube probably the overflow?

One thing I noticed and wondered about is the fuel screw. I carefully removed it and then removed the bowl and then carefully tipped the carb over so I wouldn't lose any parts. All that came out was a spring. I was kind of expecting an o ring and a washer. Maybe they were still in the carb body? I'm looking now for an exploded diagram to verify the components and the order they shoud be installed. Looking at the Merge Racing diagram it appears to be washer, spring, o-ring, fuel screw, but I'll verify. If that's correct then mine is either missing or installed out of order? Would this cause a leak?

I cleaned the o-ring and put the carb back together and tried to hook up the gas and set to prime to fill with fuel before re-installing to check for leaks and if leaking see exactly where the fuel was leaking. After a minute or two I didn't see any leaks, so re-assembled and tried it again. Before I got finished re-installing I noticed some little drips of gas definately seemed to be coming from the bowl somewhere. Reaching in and feeling for gas it seemed like it was on the bottom of the bowl. It was almost dark and I knew I might need to get some parts so I finished re-assembly and took a little test ride in the neighborhood because I just HAD to try it out. WOW, I was really impressed with the power and response of the FCR. Worth every penny, don't wait, don't wonder, don't worry, JUST DO IT!

After the ride I'm still seeing some small drips of gas, still looking like the bottom of the bowl, HOWEVER, that is the lowest point of the carb and any gas leaked could end up down there, so I'm not sure? I'll ride the DR350 tomorrow and read and think about it some more before I R&R the carb again. I definately seen to verify the parts on the fuel screw and may need to order some parts. I'll probably get a new o-ring for the bowl at the same time, but I don't think there is any problem with the float at this point.

Once I get to see an exploded view I'll also be looking for an access plug for the jets. I think there is one on the FCR? maybe a 17mm plug? If there is a plug there I'll need to check and see if it's tight and if there is an o-ring?

Are there any other places for a leak that I have not thought of?

I'm looking for a good exploded view that I can zoom in on and also has a parts list. I'll probably find one tonight, but if anyone has a good link, I'd appreciate it! The carb is a 39mm Keihin FCR MX from a YFZ450 four wheeler.

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Wow, that's a lot of words to say 'my float bowl has a leak'.

DON'T USE CARB CLEANER on MC carbs. You will ruin the oring seals (which might be your problem).

You need a fcr exploded diagram so we know what parts you are talking about when you describe them. Sudco.com

Sounds like your only problems are:

- must find/replace missing o-ring and washer for the fuel screw. Probably disintegrated up inside the passage.

- change your float needle. Many ebay carbs have float needles that are corrupt from sitting out in the air after being in gas. The rubber on the tip deforms.

- if that doesn't do it, you probably have a deformed o-ring seal under the needle seat. This is not good, as it's a real pain to replace. They too will deform.

- if it's not any of those, it's the body seal. It can be replaced, even though others will tell you it cannot. jdjet.com

NEVER USE CARB CLEANER!!! Use spray brake cleaner.

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Thanks for the quick reply! I appreciate it. Yes I use too many words, but I don't want to leave anything out that might help solve the problem. This wasn't an Ebay carb, but I'm not certain of the history with the PO. It was refurrbed by mxrob and modified with all the DR650 mods and set up for a DR650. The PO said he was using it on his DR650 and when he decided to sell he removed the mods to sell separately. I have no idea if he used carb cleaner on it or how long it has been sitting, but I think it was running on his bike this spring, so maybe 6 months? I'll try and call him again tomorrow.

I got a link to a nice exploded view on Sudco from another forum.


Looking at this diagram I found the correct order for the fuel screw is screw, spring, washer, o-ring. So I may or may not have a problem in that assembly. I'll need to look in the carb body and see if the washer and o-ring are MIA or just retained in the carb body. Even if they are there I guess the o-ring could need to be replaced.

Also looks like there is a plug in the bottom of the bowl (Drail Bolt, number 123) with o-ring (number 122) that will need to be considered.

Of course the main o-ring/gasket (Bowl Packing, number 45) could be a problem.

If gas is not coming out the overflow, can I rule out the float assembly for now? Gas seems to be coming out the bowl or where the bowl attaches to the carb. SO, I'm still thinking fuel screw, jet access plug, and o-ring/bowl gasket (Packing)

Tomorrow I'm going to check the bowl and see if it has emptied completely. If it is mostly empty I would assume the leak is near the bottom of the bowl, maybe the fuel screw or the drain plug/jet access plug. If there is still some gas in the bowl, maybe that could indicate the bowl o-ring leaking?

Since it's not leaking out the overflow, I'm not looking too close at the float assembly yet since I would expect it to come out the overflow if the float was stuck (it wasn't) or wasn't seating properly? Again I did a simple test of the float by blowing int he fuel supply and when the float lifts (not measured) it stops up tight.

I haven't considered the acelerator pump cover yet (Number 47) but I guess it's got to be a suspect since the fuel seemd to come off the bottom of the bowl. Could fuel leak from the accelerator pump cover?

Thanks Again! Please excuse the novella 👍

Edited by GaThumper

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Thanks! that will definately be part of the process Saturday. I attempted that yesterday but using the short hose from the tank and setting petcock to prime I didn't see any leaks after a couple of minutes. May not have been enough time for the leak to develop.

Saturday I'll remove the carb again and check the jet plug and accelerator pump cover and the fuel screw assembly and then fill it up with gas on the bench and see what I can find.

Appreciate the help!

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