2005 RX1 MCX rear mount

[Radioactivenewf]

Hi all,
First off, I have been reading and reading for the last week, lots of great info, but unable to resolve my issue.
Purchased this sled last week with a bottom-mid hesitation/backfire symptom. Removed carbs and found The following:
135 mains
25 pilots
Pilot screw out 2.5
Only one pilot was dirty
One carb had small o-ring missing on top cover
Main jet o-rings broken
Needles set to mid clip
Minimal debris behind seat
One inter cooler to carb boot may have leaked.
I set pilot to 2 to start. Cleaned all carbs. Replaced o-rings on mains. Added o ring missing on top cover. Set clip to bottom slot on needle. Fixed IC to carb boot.
Still having what appears to be lean condition. I don't have a A/F meter yet. If I get on the throttle hard I get backfiring and hesitation for about 1-2 sec. Until turbo spools. Then it clears up and runs great. If I ease into throttle I can get it up to RPM without backfire.
Any suggestions? Pointers, change back to stock pilots? This is my first 4 stroke sled, after riding a buds, I wanted one myself! Thanks in advance, and kudos to this great forum.
Edit: I will be testing at about 2200'. Again, if anyone can direct me on what starting point for jet sizes ect I need as I can't find any info. Even a link so I can read more, anything.

 

[BigDog05]

How much boost are you running? I would put all the carb settings to stock. One thing to check is the tension on the waste gate rod. Mine did the same thing early on. You want a little tension on the rod so the waste gate doesn't flutter. I have a Bender Stage 2 but it is very similar to your MCX.

I ended up with all stock carb settings except for main jets. I run 130 Mains and ride at 2000- 2800 ft elevation. Leaks are the biggest problems. Do you have billet T's ?

 

[BigDog05]

rxrider had a complete post on his mcx turbo, but I can't seem to find it. Maybe he will see your question.

 

[Radioactivenewf]

Thanks for the reply BigDog, from the gage it looks like I have about 8lbs or so. It doesn't have billet tee's. But if that's an inherent problem I will likely get some. There must be a site sponsor that supplies them.... I have called all over my area looking for the 17.5 pilots, couldn't find any Saturday. They should be in early this week. I will check the wastegate for sloppy rod and adjust if needed. Is there a certain amount or number of turns after the slack has been taken up? Thanks again.

 

[givemeaboost]

I would never run a turbo Yamaha engine without having a good air/fuel gauge and learn what are acceptable readings. One small mistake and the block is trashed. I've got two of them to prove my point.

Ken......

 

[Jbat]

I would never run a turbo Yamaha engine without having a good air/fuel gauge and learn what are acceptable readings. One small mistake and the block is trashed. I've got two of them to prove my point.

Ken......

Exactly, get an a/f ratio gauge, preferably wideband so you can tune it properly

 

[silver rocket]

Hi all,
First off, I have been reading and reading for the last week, lots of great info, but unable to resolve my issue.
Purchased this sled last week with a bottom-mid hesitation/backfire symptom. Removed carbs and found The following:
135 mains
25 pilots
Pilot screw out 2.5
Only one pilot was dirty
One carb had small o-ring missing on top cover
Main jet o-rings broken
Needles set to mid clip
Minimal debris behind seat
One inter cooler to carb boot may have leaked.
I set pilot to 2 to start. Cleaned all carbs. Replaced o-rings on mains. Added o ring missing on top cover. Set clip to bottom slot on needle. Fixed IC to carb boot.
Still having what appears to be lean condition. I don't have a A/F meter yet. If I get on the throttle hard I get backfiring and hesitation for about 1-2 sec. Until turbo spools. Then it clears up and runs great. If I ease into throttle I can get it up to RPM without backfire.
Any suggestions? Pointers, change back to stock pilots? This is my first 4 stroke sled, after riding a buds, I wanted one myself! Thanks in advance, and kudos to this great forum.
Edit: I will be testing at about 2200'. Again, if anyone can direct me on what starting point for jet sizes ect I need as I can't find any info. Even a link so I can read more, anything.

I have a 2003 RX1 MCX Rear Mount and run with stock jets and needle set to mid clip, pilot screw at 2.0 turns. Should run fine at your altitude. I ran mine at 6,000ft to 9000 with 130 mains. I have holtzman green springs in the carb. I run 12 psi and I have the head shim and slotted cam gear as per MCX instructions. It's on the edge of detonation at 12 psi with 91 Octane. The kit was designed to run at 10 psi with the head shim. Do you have the head shim installed? Check your throttle cable adjustment.

 

[Radioactivenewf]

Ok, update: I got all the carb back to stock settings, I have what looks like plastic "tees", I am unsure but suspect you are talking about the ones Btwn the carbs that branch off and go to the IC. If so are they so prone to leaking and causing my condition? I checked the linkage on the wastegate and it does not seem loose whatsoever.
For the head shim, is there a specific way to tell it from stock? I am very unaware of what work has been done to this sled but am learning quick. I did adjust the throttle play as it was sloppy when I first took it out but it has not made any difference. The throttle override switch has been disconnected anyway, I guess this is why you ask about the throttle cable. I am still thinking about which a/f gage to pick up, any suggestions/price range?
Also, the spring in the top of the carb, would it also give me these symptoms?
I will be putting the carb rack back on tomorrow or Saturday but the weather is very warm and may affect the changes made also.
I will keep posted and likely ask more questions, thanks again and happy sledding!

 

[BigDog05]

I would try and find billet T's. Most guys had problems with the stock plastic ones. I've had good luck with the AEM wideband A/f gauge. Sensors don't last real long with racing gas mix. As long as you have the plastic T's are they glued good?

 

[BigDog05]

How many hoses do you have going to the back of the carbs? Originally on the Bender kit there was one hose going from the inner cooler to the 2 back pairs of carbs. Some of us changed that to 2 hoses going to the backs of the carbs. One hose to each pair of carbs. If you have one hose going to both pairs, and you blow into the hose, you can see that the slides don't all open at the same time.

 

[sledheadgeorge]

Could be the "t"s Try spraying them with brake cleaner while its running to see if they leak.

 

[Radioactivenewf]

Ok great tips guys. I have plastic tee's and tried spraying them at idle with brake clean, no change in idle RPM. I got carb all setup back at stock settings with exact same symptoms, good start, good idle, punch the throttle and it starts to gain RPM for the first half sec until it falls on its face and hesitates/backfires. One thing I didn't mention is that if I turn the idle up to about 1500, when I touch the throttle it will hang at about 3-4k RPM. Then I have to turn back the idle screw till it gets to about 11-12hun.
As someone suggested, I will next try it with the choke partially on. I will also check the TPS readings. Would the TPS have the ability to cause these symptoms??
Good thing it's warm and virtually no snow here or Id have the itch to ride the beast and be even more pissed with it. After I try the choke and TPS numbers I'll keep you posted on results. Cheers!
Edit: there are two hoses for pressure going to the carb from the IC that control the slides, both carbs from both sets open same time. It also backfires after it is shut down.
So I pulled the fuel tank and tried some bubbles on the donut gaskets to ensure they are not leaking either. They seem fine while i let it run for a few seconds.
Has anyone had problems with the actuator on the inter cooler not functioning properly? I'm grasping at straws at this point.

 

[givemeaboost]

AS I said before you need a good wideband. You need to find out if it's lean and at what throttle and boost is doing at the time. These engines don't like to be lean when the boost is up. They melt pistons. I tried using a cheap narrow band A/F gauge and fought with it for the better part of two seasons till I put a wideband on it.

Ken............

 

[silver rocket]

AS I said before you need a good wideband. You need to find out if it's lean and at what throttle and boost is doing at the time. These engines don't like to be lean when the boost is up. They melt pistons. I tried using a cheap narrow band A/F gauge and fought with it for the better part of two seasons till I put a wideband on it.

Ken............

Ok great tips guys. I have plastic tee's and tried spraying them at idle with brake clean, no change in idle RPM. I got carb all setup back at stock settings with exact same symptoms, good start, good idle, punch the throttle and it starts to gain RPM for the first half sec until it falls on its face and hesitates/backfires. One thing I didn't mention is that if I turn the idle up to about 1500, when I touch the throttle it will hang at about 3-4k RPM. Then I have to turn back the idle screw till it gets to about 11-12hun.
As someone suggested, I will next try it with the choke partially on. I will also check the TPS readings. Would the TPS have the ability to cause these symptoms??
Good thing it's warm and virtually no snow here or Id have the itch to ride the beast and be even more pissed with it. After I try the choke and TPS numbers I'll keep you posted on results. Cheers!
Edit: there are two hoses for pressure going to the carb from the IC that control the slides, both carbs from both sets open same time. It also backfires after it is shut down.
So I pulled the fuel tank and tried some bubbles on the donut gaskets to ensure they are not leaking either. They seem fine while i let it run for a few seconds.
Has anyone had problems with the actuator on the inter cooler not functioning properly? I'm grasping at straws at this point.

Did you check your fuel pressure regulator. Hook up à pressure gauge to your fuel line. I have mine set at 3 psi at idle. Take it for a spin and watch your fuel pressure, it should always be higher than your boost pressure by at least 5 psi.

 

[sledheadgeorge]

Forgot to mention if your carbs and plumbing is ok, you might want to check the timing. A huge backfire can cause the timing chain to skip a tooth.