Airflow to carbs?

[redmike]

I have a 1981 GS1000GL with 12 K miles, a 4 into 1 exhaust and Accel coils and wires. Everything else is stock. I just put on the K&N pods and could not get the bike to run. I gave the bike to a mechanic who adjusted the valves, repacked the exhaust and installed the Dynojet Stage 3 jet kit. The bike runs beautifully....except for one issue.

At the higher RPM's (5-8K) at a higher speed the bike bogs down and then takes off again. The problem occurrs at 50 mph and above but does not seem to occur at slower speeds, even at the higher rpm's.

I rode it and noticed that when my legs are tucked in tight, the problem does not occur. When I ride with my legs open is when the problem rears its ugly head. I have been told that I have fluttering carbs which means that when the airflow is blocked by my legs the bike runs fine but when the airflow is disrupted riding in an open position, the bike bogs down at higher rpm/speed.

My mechanic suggested creating a "shield" out of metal which would help the airflow to the carbs be more consistent (like when I ride with legs "tucked in") or go back to the stock airbox. Has anyone out there had this experience and if you did how did you deal with it? Any ideas would be greatly appreciated.

Thanks so much

Mike

 

[Steve]

You started this exact thread yesterday. :-k

.

 

[Jethro]

Personally, I never liked aftermarket pods. I went to great lengths to bring my bike back to stock. I never was able to make pod filters run absolutely perfect, and that is unacceptable to me. That said, I never heard of how your legs are against the bike to affect the way the pods run. I see Steve (in your other thread) has stated that it has been shown that pod filters can prevent airing your bike correctly- that shocks me. I can't see how your legs can affect that much air from getting to your carbs at all. Not saying it's not true, I just don't see it. You may need to oil your pods better or your jetting is incorrect. There are circuits to the carbs, idle, low speed and high speed. It sounds to me that the transition from low to high speed circuits is not good.

 

[hampshirehog]

Right - found your thread so let's see if I can help.

Jethro is bang on about pods and CV carbs. I've been 'forced' down this route a few times (due to missing original airboxes) and I have never managed to get a bike to run faultlessly throughout the rev range / throttle opening range. I can get 'em pretty close put never spot on (though some guys have).

I've never experienced your precise problem with pods but I have with bellmouths (aka velocity stacks). I must make a video of it but my mate has an A65 fitted with bellmouths and on a windy day on tickover his revs are up and down all over the place. We've fooled around with bits of cardboard and found that any guard has to be very close to the inlet. I guess if we made up something it would be pretty close to the guard on this foam filter:

 

[BassCliff]

Hi Mr. redmike,

I'll relate a similar experience.

Last summer I visited the Indianapolis area for the MotoGP. Mr. Griffin loaned me his very nice '81 GS750E to ride while I was in town. I was staying about an hour away and commuting to IMS for the races. One morning while riding the interstate into Indy, unbeknownst to me, the right sidecover blew off. The bike would hesitate and surge whenever a gust of wind would blow. When I realized what had happened I did the same thing you did, I held my leg close to the sidecover which blocked the wind. Later, I put the right carb vent hose where it would be less susceptible to turbulent wind. The bike rode fine after that.

Where are your carb vent hoses? Do you still have them? Or are your vent tubes blocked off? If you still have your carb vent hoses, try routing them somewhere that is in relatively calm air, like under the seat in the battery box.

That's my story and I'm sticking to it.


Thank you for your indulgence,

BassCliff

 

[49er]

Hi Mr. redmike,

I'll relate a similar experience.

Last summer I visited the Indianapolis area for the MotoGP. Mr. Griffin loaned me his very nice '81 GS750E to ride while I was in town. I was staying about an hour away and commuting to IMS for the races. One morning while riding the interstate into Indy, unbeknownst to me, the right sidecover blew off. The bike would hesitate and surge whenever a gust of wind would blow. When I realized what had happened I did the same thing you did, I held my leg close to the sidecover which blocked the wind. Later, I put the right carb vent hose where it would be less susceptible to turbulent wind. The bike rode fine after that.

Where are your carb vent hoses? Do you still have them? Or are your vent tubes blocked off? If you still have your carb vent hoses, try routing them somewhere that is in relatively calm air, like under the seat in the battery box.

That's my story and I'm sticking to it.


Thank you for your indulgence,

BassCliff

I second that advise Cliff. The ideal remedy is to leave the stock length vent hoses on and direct all of them down into the swing arm pivot area, just in front of the wheel guard. The length of the tubes and the position helps to reduce the influence of turbulence/air pressure changes in the float bowls.

If you need a challenge, keep tuning to the pods.

 

[salty_monk]

Never had that issue on either of mine both with pods & both run great...!

No vent hoses & Dynojet kits in them. One is CV carbs one is VM.

 

[Ant]

Reading this has helped me greatly.

Reading this has helped me greatly.

Just installed pods on my bike without jetting or anything. They look good so I had to have them. If only I knew then what I know now!!

Needless to say, stock air box will be reinstalled tomorrow.

 

[Ant]

Here's my pic.

Here's my pic.

Say goodbye to those pods.

 

[wrgum]

I've had a similar issue w/ my 81 GS650G. When driving at speeds above, say, 50mph, and when hit directly with a stiff crosswind from the right (hitting the right side of the bike) I experience a deceleration and noticible change in engine sound. Almost a popping or, perhaps more like I came off the throttle without disengaging the clutch (pulling the handle in). Initially I replaced the o-rings and boots. I experienced the same once again a few weeks ago on the way to the lake. This thread has pointed me toward the vent tubes. I've repositioned them, and will perhaps clamp some sort of baffle on the ends of the tubes if the repositioning doesn't do the trick right away. Will let you know if it works out!

wrgum

PS. It's got stock intake.

 

[don_gibb6512]

Say goodbye to those pods.

Are those K&N ? If so, I'd be interested in buying them from you if the price is right and they'll fit an '80 GS1000G.

Thanks.

Don

 

[redmike]

wrgum,
let me know what you did and how you make out. And thanks for the reply.

Mike