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'81 XV750 Dynajet stage1 SUPER RICH!

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'81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Mon Apr 08, 2019 8:36 am

Recently got my project up and running. Did a Stage 1 Dynajet jet kit and it's running very very rich. I can turn the pilot screws all the way in until they're seated and it doesn't even phase the motor. Also won't idle without me having to maintain RPM's. When riding, i can very slowly ease on the throttle with a little bit of spitting and sputtering from the motor but as soon as i give it a normal amount of throttle, it bogs down. I got rid of the vacuum petcocks (no longer have the stock tank) and rubber capped the vacuum ports on the carbs. I haven't pulled the plugs but judging by the amount of black smoke from the exhaust, i'm sure they're toast. Should i take the caps off of the vacuum ports to see if i can get more air into the carbs? Anybody ever experience something like this before?

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: bstig60 » Mon Apr 08, 2019 8:49 am

From your description, it would appear you have at least two problems. The first thing I would suggest is to check the O ring in the pilot screw. Either they are bad or the low speed circuit is plugged up in the carbs. Does the bike idle at all without choke? The bogging down could be a vacuum leak somewhere. How are the needles set?
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Mon Apr 08, 2019 9:23 am

It barely idles with full choke. I test rode the bike with the needles set 2.5 turns out (factory standard from what i understand?), then 1.5 turns out, then again with just half a turn. I really couldn't tell if any of the changes made a difference when riding.

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: chrismalm » Mon Apr 08, 2019 12:42 pm

:yup:
"Choke" is a common term for the fuel enrichment circuit. If it dies off "choke" and your pilot screws are ineffective, your engine is getting fuel from the enrichment circuit and the pilot circuit is not functioning properly. Search the archives for tips on cleaning and adjusting your Hitachi carbs. Also check the resistance of your plug boots and repair or replace as necessary.
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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: Flyingdog » Mon Apr 08, 2019 7:53 pm

:yup: :yup: :yup:

Won't run without choke..pretty telling. Besides the starter enrichment circuit, those carbs could be trying to suck some fuel thru the needle jet if the pilot is really clogged.


abond125 wrote: Anybody ever experience something like this before?


Only with a Dyno Jet kit. :bg:

Personally, I wouldn't touch a Dyno kit, unless ya gottsa pretty radical engine on you hands, but that just me. Piddled with dyno kits yrs ago, just to see. Really only thing tough was getting that jet needle dialed in (along with the mains). Found better fine adjustments with different needles than adjusting the one they give a. Don't remember if the Dyno needle's taper was different than stock or what. Not tough, though, just some fiddl'n. Just more than what's actually needle on stock carbs. Doing a plug chop..should tell ya fairly quickly. Least it should tell ya if your at one extreme or the other.
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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Mon May 13, 2019 8:34 am

OK so....
I put all of the stock parts back in the Hitachi carbs. All of the vacuum ports are plugged. The setup is: K&N filter where the airbox used to be, stock carbs (minus all the vacuum mumbo-jumbo), 2 into 1 exhaust. Still ran very rich. I even took the rubber air intake boots off of the carbs so they're getting as much air as possible and it's STILL RICH!!! I don't get it. The pilot screws are only about a quarter of a turn out. It should be so lean that I'm burning valves.

Oh and thank you, btw, for everybody who has replied. I appreciate it!

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: Flyingdog » Mon May 13, 2019 8:51 am

What's your altitude? What are the main jet sizes (I assume the needles are back to stock)? You checking just at idle'n/blip'n throttle? Have you done a plug chop? Remember, when actually riding, pilot screw will have very, very little effect. You'll be on the needles any time you're moving. The pilot will give ya that smooth transition from idle to off idle. IMO: that's it. But even chart like these, show the pilot more influential. I think it too generous, but that's me. There's vids out there showing fuel intake at various throttles, only time you see anything com'n outta pilot circuit is at idle. But like tires, plugs and oil..opinions will always vary.
Have you checked you're emulsion tube (aka: needle jet)? Very common for them to get outta round (they're just brass)..possible excess fuel is seep'n by the needle at all throttle positions (idle > WOT). Have you looked into the carbs' throat, see if anything looks unusual when running?
There's something else I ran across, once, that drove me to the edge. Did everything I could think of and by chance, noticed on the 750 the snorkel tube, under the seat, would actually suction itself to the seat pan at certain rpms. That was one for the books.

And...as Chris said..don't overlook the electrical portion of the equation. Coil, caps, plugs, wires, clean/shiny connections throughout..etc etc etc.
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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: bstig60 » Tue May 14, 2019 9:38 am

abond125 wrote:OK so....
I put all of the stock parts back in the Hitachi carbs. All of the vacuum ports are plugged. The setup is: K&N filter where the airbox used to be, stock carbs (minus all the vacuum mumbo-jumbo), 2 into 1 exhaust. Still ran very rich. I even took the rubber air intake boots off of the carbs so they're getting as much air as possible and it's STILL RICH!!! I don't get it. The pilot screws are only about a quarter of a turn out. It should be so lean that I'm burning valves.

Oh and thank you, btw, for everybody who has replied. I appreciate it!


The pilot screw O rings are shot or incorrectly installed. You cannot run at low speed without choke on, you turn the pilot screws all the way in and it has no effect on the engines running, you are running full rich. Take a hint from the replies to your posts telling you what to check.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
It is easier to help you if we know where you are.


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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: Flyingdog » Sun May 19, 2019 2:06 pm

abond125....

Have any success/failure/new vocabulary?
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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Tue May 21, 2019 8:13 am

Sorry everybody. I'm in the middle of a kitchen renovation so my motto for the past few weeks has been, "Happy wife, happy life."

I'm in southeast Pennsylvania so my altitude isn't anything special.

As far as doing a plug chop, I did not because when I'm riding, I can't get to full throttle. I probably can't even get to quarter throttle before it gets too loaded up with fuel and boggs out.

Whenever I'm allowed to have my life back, I'm taking the carbs off and checking the o-rings since that sounds like the easiest thing to do first.

Assuming everything (stock carb components) is looking good, what would you suggest checking next?

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: bstig60 » Tue May 21, 2019 3:50 pm

If it were me, I would remove the Dyna Jet kit. I had one in mine when I bought it and never could get the carbs properly adjusted. I removed it and went back to stock Jets and needle, adjusted and synced the carbs and there have been no more issues. That was 10 years ago.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
It is easier to help you if we know where you are.


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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Wed Jun 05, 2019 7:57 am

OK so again, all stock components have been put back in the carbs. It is running just as poorly as it was when the jet kit was installed. I will check the o-rings on the pilot jets when I get some time to see if that corrects the idle/low rpm circuit richness. The vacuum petcocks have been replaced with regular gravity fed petcocks and all of the vacuum lines have been removed and vacuum ports plugged. The airbox is also removed and has been replaced with an oval shaped K&N filter. I can still only make it about a quarter of a mile before the spark plugs are fouled. During that quarter mile, the bike can only handle a tiny bit of throttle at a time, spits, surges, and backfires through the air intake occasionally.

Can i change the title of this thread to say "Almost Stock Hitachi Carbs Running Super Rich"?

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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: bstig60 » Thu Jun 06, 2019 2:52 pm

Could be your chokes are leaking and/or not fully closed. If memory serves, on the Hitachi's, the choke actuator comes out and it has an O ring on it. If that seal is bad, then the chokes will leak fuel into the venturi and make it run rich.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
It is easier to help you if we know where you are.


SERVICE MANUAL DOWNLOAD LINK
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Re: '81 XV750 Dynajet stage1 SUPER RICH!

PostAuthor: abond125 » Fri Jun 07, 2019 8:09 am

I'll check that out also. Thank you!

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