83 XJ750 from Brenny's runs great, just doesn't start without holding throttle

OK. The 83 XJ750 from Brenny's arrived last Wednesday and after some fits and starts, I've been able to ride it over 300 miles. The bike looks very good and really runs great -- once it's warmed up. So far, for the life of me, I have not been able to figure out how to set the choke so that when I first start it up it will keep running. It starts up when I roll on the throttle, runs for about 10 seconds and then cuts off, unless I hold the throttle for at least a minute or two to keep it running. I have a cheap throttle lock so that helps -- I just rev it up to around 3,000 rpm, push the throttle lock against the brake lever, then watch the rpms slowly drops down, then I rev it again, set the throttle lock...wash, rinse, repeat. I've tried all possible positions for the choke, from none to full, and it makes no difference. (The weather here has ranged from around 55 at night to around 85 max during the day.)

Once it's been running for a couple of minutes using my "system", it runs perfectly thereafter, idles around 1,200 rpm (which is fine as far as I'm concerned), and gets 38 to 42 mpg, depending on what kind of riding I'm doing. It never stalls, and when I stop to get gas, turn off the engine, and finish filling the tank I can restart the bike with no problems. I think the idle is set properly. And I don't see how the carbs can be bad/dirty when the bike runs perfectly the rest of the time. It's only at start up. Could it be that the choke is somehow bad or needs to be adjusted or replaced? I'm kind of at a loss. Anyone else have this kind of experience? As always...thanks in advance.

 

https://www.xjbikes.com/forums/threads/how-to-clean-the-enrichment-circuit-well.8918/

Check this link out it is under Forums go to XJ how to do instructions where there is a lot of great information on these bikes.

 

Thanks much. I will do that. (A buddy of mine who works on his 3rd gen Magnas looked at the bike and told me that even though it runs great after it's warmed up, that doesn't mean that the carbs still don't need to be cleaned. I was a little surprised, but he definitely knows his stuff. He did confirm that the physical choke mechanism is engaging, and as soon as he saw that he said it's most likely a carb issue.)

 

True if the enrichment circuit is not working properly when the engine is cold it won't start. When it is hot it will start because it does not need a rich mixture which can create the illusion the carburettors do not need cleaned. As you will see Chacal has a small drill for clearing the enrichment circuit at the bottom of the float bowls.

 

Those enrichment tubes are really prone to blocking, as are the galleries in the float chamber (well this is true for the mikunis - are the hitachis also thus prone?
Also to add, the enrichment device isn't a choke as in some other carbs (my kehins for example), and are dependant on their own jets, hence the issue.

 

Intake gaskets, manifolds and throttle shaft seals! And of course " church of clean"
Just changed gaskets and manifolds on my Xj750rl.

 

Try giving your carbs a "hotshot" pull the fuel line , drain the float bowls . Get a meat baster syringe fill it with a mixture of Berrymans B12 carb cleaner and acetone inject it into the fuel line fill several times let sit for about half an hour. Now drain the float bowls reattach the fuel line put petcock to PRI and let it fill for a few minutes set the fuel enrichment to about half and try to start ...it may smoke for a few minutes if this does not help....You will need to pull your carbs , the tiny jet in the float bowl is plugged . But sounds like you need to take carbs to church cheers

 

Thanks. And speaking of the petcock...the petcock on this 83 is very different than the one on my 82. First of all, what is PRI? Second, if rotation is the same on both bikes (which makes sense -- clockwise to get to reserve/counterclockwise from reserve to get back to the regular tank) -- the "Fuel" arrow points UP towards the reserve tank when it seems like the dial is positioned for the regular tank. I want to make sure I've got it in the regular position, not the reserve position, at least until I get more familiar with the range of this bike.

 

Good chance you have a aftermarket petcock does it have a vacuum line from number 3 cylinder to petcock? On the stock On only flows when engine is running . PRI & RES flow fuel constant . The ON function is a desirable feature because this will keep from possibly flooding the engine of you have a float needle stick .

 

I'll have to check about the a vacuum line from the number 3 cylinder. (And when I can I'll post a photo. It's a used bike so I don't know if it's a stock petcock or aftermarket.)

 

OK. Here's a photo of the carb kit I just purchased. (There are obviously 4 of them, one for each carb.) From the photo, does this kit contain everything I need, or do I still need to purchase the jets for the enrichment device separately? And if so, where are you guys getting your carb kits? Thanks. And the link to Chacal's Starter Jet Clean Out Drill Bit isn't working.

 

No this does not contain the butterfly seals you can get them from xj4ever ...listen if you do your carbs right the first time you should not have to tear into them again for a long while.

 

Thanks.