Rpm drops

[magna_dude74]

Hello All,
So I have been riding into work alot lately and I noticed something strange on the highway with my 1994. When I roll into the boost real slowly, I can see / feel / hear the RPM's jump up when the boost kicks in around the 6K mark, but then at around 7500 RPM it acts like an automic transmision and the RPM's drop down to around 7K RPM. I have done this consistantly for the past couple of days, and now it is realy starting to bug me.:bang head: The throttle response is spot-on, and the only other thing I noticed, and this just happened this morning, I am getting alot more of a rumble when I roll off throttle. Some call backfiring, but not like a car, no "BANG, just louder rumble that is not uniform in sound or tone. I am going to check the Jardine connectors to the header and see if one is slipping off. Everything else motor wise is stock. Another thing I noticed is the exhaust smells real bad, you know the smell when you use a little too much Seafoam? I know it is probably time for new plugs, and the carbs had a sync job a couple months ago, since then I am getting 40+ MPG.
Thanks in advance for your thoughts and opinions....

 

[wildweasel_pt]

Check the Vboost system. Linkages and butterfly operation as well.

 

[alorio1]

I would change the fuel filter, drain the carb bowls, check the fuel vent line on the tank and also blow air back thru the fuel inlet on the tank. If either of the tank lines have a restriction the fuel pump will have problems getting fuel to the carbs. Only cost you will have is a new fuel filter and this take a lot out of the equasion of trouble shooting the problem.........

 

[naughtyG]

Take a good look with a bright flashlight inside your tank to make sure there is NO rust.

What happens after it gets back to 7ooo rpm, does it then pick up again? Can you still get it past into higher revs? Does it do it while accelerating or only when cruising @ 7.5k?

 

[tugla]

did this symptom just start or been on going with the bike?

 

[magna_dude74]

Thanks for all the advice everyone!!! The RPM is spot on with the throttle, when it drops down I just barley move my wrist and I am back at 7.5K. Then if I want I can take it as high as I want it to go. The throttle/rpm ratio is spot on and is EXTREMLY touchy, maybe it's just me relaxing ever so slightly on the throttle that is causing this. Like I said in the beginning I was checking a SLOW roll on and not WOT. I should do a gas filter/ plug change as it has been a couple years now. I am running the Iradium plugs because I thought they would be the last plugs I would buy. What is a good plug for my stock motor with Jardines? Thanks everyone

 

[alorio1]

I always run NGK plugs (DPR8EA-9) , you also might want to check to see if the air box is seated on all four carbs and clamps tightened. If the airbox is not properly seated, the CV carbs we have on our Maxes the slides will not respond properly to throttle position.

 

[magna_dude74]

Cool thanx for the plug info. I have never had the air box off only the air filter for cleaning.

 

[magna_dude74]

WHAT THE HELL IT'S GETTING WORSE!!!! So no I get backfire from the left exhaust, so what is that cylinders 2 & 3? I put 1oz of Seafoam and let it idle in the garage for about 1/2 hour then took her out on the highway. I get "POPPING" at around the 3000 mark, nothing above that until I decel. I just realized the other night I rode about 12-15 miles after my fuel light came on, I never go more than 1-2 miles when the light comes on. You think I sucked some shit up from the. Otto
Of the tank? No local shops have the fuel filter so I am going to have to get online, if it's not too late. What else should I check, knowing that I am getting backfire/popping at a constant throttle?????

 

[magna_dude74]

Ok so I went out to look at the choke linkage, thinking maybe something was hanging up. Everything moved freely, but I did notice oil on the left (sitting on bike) rear carb. so I opened the cover and air box to take a look. Sure enough there was a pool of oil on left side of the air box!!! looks like the oil soaked through and down the outside of the carb, strange I'm thinking to my self.... So I started the bike to see what I could see. First time I hit he starter button a Big -O-Cough came through the right rear (sitting on bike) carb. Hit the button again and she fired up. Now I'm shining the light in each carb and I notice the same carb that coughed is weeping fuel out of the needle/jet. I also noticed the slides don't move unles I rev the motor, then they all slide like they should. When I tried to WHAK the throttle it almost stalled, but slow roll and the carbs seamed to work fine. Ireved up to 3000 RPM and no backfire until I let off & then only one or two "POPPS" , so I'm thinking the air filter is no good or the carbs are running to rich.so....

Why did the carb cough and spit back????

Why did the motor fall on it's face when I cracked the throttle open?

Should the slides be moving/actuating at idle?

Should I see fuel weeping from the needle/jet?

Thanks all...

 

[naughtyG]

When you open the airbox (or take it off) the motor won't run good at all, in fact it'll conk out as you rev up (too much air without the airbox)

It sounds like your carbs need a good clean - it may be that the Shogun/Peashooter will do the trick, but on a '94 they're most prolly due for a good clean up + checking all rubber parts and replace as needed. It's not hard to do - there's a full 'how-to' with photos I made a coupla years ago when I did my '86 in the carbs section.

 

[magna_dude74]

Thanks everyone, I think a rebuild is in order. Never doing this before I am going to see if I can get someone around me to watch over me as I do to make sure I don't miss anything small, like pinched fuel line or something like that.

 

[alorio1]

If you have a digital camera take lots of pics during dissasembly, that always helps me when going into unknown territory......

 

[magna_dude74]

Hello all,
Here is an update for you......
Switched the plugs again, to the correct NGK plugs,Advanced Auto sold me the
WRONG PLUG, I will be having words with the manager when I return them.
I did change the fuel filter
I did notice the airbox was raised about 0.250 compared to the other three
carbs, and both clamps on the left side were loose, they are now tight and
airbox is level.
I was able to spray some B-12 as close to the choke vent tube and the PAJ1as
possible with the bottom half of the airbox still connected, as well as the rest
of the carb throat.
I blew out all four vent tubes and it blew liquid gas back into the carb and
finally some air once cleaned out.
The idle is much better now, and the raw fuel smell is gone. There was a short
ride and no popping occurred, so hopefully all these things took care of it.
Special shout-out to Damon for walking me through my fixes......

 

[alorio1]

Happy things are getting better, I bought some plugs (automotive) once from autozone and they were the wrong type but I did not notice it untill check engine light came on. They would not let me return them even though the clerk sold me the wrong plugs.

 

[magna_dude74]

Sorry to hear about your experience with Autozone, at least Advanced Auto will take just about anything back. Hopefully it didnt do any other damage farther down the line, like an O2 sensor or something.