78 gs750 Air Box Question

[sparkey]

Another question about this wonderful bike. The stock airbox is missing the rubber intake on the back of it so it is basically just a metal box to look good.. Bought a KN filter as the other one was a rats nest. The bike is running to lean and wont get past 6 or 7k at WOT. It does have stock exhaust. Carbs have been cleaned and valves checked. Does that rubber intake on the back create enough resistance to make it run like shazit with it gone?
Brian

ps: i did drop the washers on the needles and it had no effect....

 

[7981GS]

Does that rubber intake on the back create enough resistance to make it run like shazit with it gone?
Brian

Yes. Try going up 2 sizes on your main jets. One might be enough.

Daniel

 

[Suzuki mad]

With poor running at high rev's indicates that the mains are too small in that set up. I dont know how far a jet to go up too, sorry.

 

[sparkey]

http://www.jetsrus.com/a_jets_by_carburetor_type/jets_mikuni_VM11-22_main.htm

do these look like the right ones? I will probably try 120's or maybe a jet kit with multiple sizes so i have them all to try out..
I might as well buy a set of pod air cleaners for it seein it is kind of one big pod right now..

 

[49er]

Save yourself some grief and find a replacement snorkel. If you don't, be prepared to experiment with all the jet circuits before it will run sweetly again.

 

[sparkey]

Save yourself some grief and find a replacement snorkel. If you don't, be prepared to experiment with all the jet circuits before it will run sweetly again.

Found one on ebay for 35 bucks. what a rip off i will fab something up for that price. I dont mind experimenting with different jets. As a matter of fact when i took the carbs apart they had 3 different needle heights. So i am in for experimentation anyway... (these were carbs that were bought from a parts yard and not originally on this bike.)

http://cgi.ebay.com/ebaymotors/1978...rcycles_Parts_Accessories&hash=item43a645223b

 

[chuck hahn]

Debunking the snorkel MYTH...The snorkles ONLY FUNCTION is to make the airbox get its air from above the swingarm and inner fender mud flap..If theres just an open hole then road slop can get sucked in easier than if the air is drawn in from above. It has absoutely no effect on anything other than that. Now for some advice from someone who has both the B and E models.. Go to BASSCLIFF WEBSITE and choose the 750 ( 8 valve ) service manual down load. Page 16 has the stock jet sizes. The clip will go on the CENTER groove on the needles. Check all the numbers from the manual to what your carbs currently have in them. Set the pilot screw ( on the bottom ) at 1 1/4 out. I know it says 1 in the manual but trust me here. Then set the MIXTURE screw ( on the side ) at 1 1/2 out. This will get your basic set up and the bike will start right up. Be sure that a proprly done bench sync is done before installing them.

 

[sparkey]

Debunking the snorkel MYTH...The snorkles ONLY FUNCTION is to make the airbox get its air from above the swingarm and inner fender mud flap..If theres just an open hole then road slop can get sucked in easier than if the air is drawn in from above. It has absoutely no effect on anything other than that. Now for some advice from someone who has both the B and E models.. Go to BASSCLIFF WEBSITE and choose the 750 ( 8 valve ) service manual down load. Page 16 has the stock jet sizes. The clip will go on the CENTER groove on the needles. Check all the numbers from the manual to what your carbs currently have in them. Set the pilot screw ( on the bottom ) at 1 1/4 out. I know it says 1 in the manual but trust me here. Then set the MIXTURE screw ( on the side ) at 1 1/2 out. This will get your basic set up and the bike will start right up. Be sure that a proprly done bench sync is done before in stalling them.

Sounds good.
Another question then: Why even have an airbox (that everyone on this site tells us to seal it up with no leaks at all!) if a big gaping 1 foot 2 inch hole in the back doesnt mean anything.
What you are saying is that no-one need to re-jet after putting pods on it, which basically is what I have right now.
It has stock jets and needles and have set all the screws up to no avail.
Brian

 

[earlfor]

Sounds good.
Another question then: Why even have an airbox (that everyone on this site tells us to seal it up with no leaks at all!) if a big gaping 1 foot 2 inch hole in the back doesnt mean anything.
What you are saying is that no-one need to re-jet after putting pods on it, which basically is what I have right now.
It has stock jets and needles and have set all the screws up to no avail.
Brian

The snorkel provides a specific air inlet area. Without the snorkel, the hole is bigger and you get a lean mixture. Block off the hole too much and you get a rich mixture. True, you do not need the snorkel for the bike to run IF you keep the same size intake hole in the airbox as you would have had with the snorkel. As said, it does help to keep the intakes from ingesting road dust and crap.

Earl

 

[chuck hahn]

By " sealded off" It means the gaskets on the cvoers are secured and all the seams that make up the box structure are sealed with some silicone or whatever sealer you choose. This makes the airbox draw air from..and only from..that gapping hole in the back. And Earl. I ran my 77 without the snorkel for nearly a year before I realised there was something missing. And yes this was my first gs. I got a snorkle and insatlled it and it didnt change any setting or effect the running in any way..nuttin nodda. I call BULLCHIT!!!

 

[sparkey]

gonna try some experimental duct tape to make the hole smaller till it runs good. I do have a snorkel from my 850 but it is way too big..



Bullchit has been called watch out! lol

 

[chuck hahn]

The overall thickness of the rubber is around 1 MM..Now the boot has a groove in the bottom that the airbox metal slips into..right? Well do you really think that decreaseing the edges of that hole by 1mm really matters..Not. I am seriuos here...dont even waste your time or the tape. Go to the bikecliff site and be sure you have the 100 mains and the 5F21-3 needles and set up the carbs as i told you.. it will start right up, and have more response and power than youve ever known it had. But then again you can fall for this witch doctory and waste your time..your call.

 

[earlfor]

By " sealded off" It means the gaskets on the cvoers are secured and all the seams that make up the box structure are sealed with some silicone or whatever sealer you choose. This makes the airbox draw air from..and only from..that gapping hole in the back. And Earl. I ran my 77 without the snorkel for nearly a year before I realised there was something missing. And yes this was my first gs. I got a snorkle and insatlled it and it didnt change any setting or effect the running in any way..nuttin nodda. I call BULLCHIT!!!

Chuck, it would depend on where and how the snorkel was cut off. If you cut the end, it wouldnt change anything. If you cut a hole in the airbox and around the base of the snorkel, it will make a big difference. I did say that there would be no difference IF the throughflow area remained as original didn't I?

If air intake area made no difference, then all those guys that removed their air boxe, installed pods and rejetted for no reason are going to be miffed.

Earl

 

[sparkey]

This is not a small little hole we are talkin about here. It is the almost same length as the filter and half as wide, you look in there and can see the whole filter from one angle. It is a K&N filter besides so it has less draw than a stock one in the first place.
Maybe i should just buy pods and rejet and the myth and ambiguity about the airbox will go away.. =)

 

[earlfor]

This is not a small little hole we are talkin about here. It is the almost same length as the filter and half as wide, you look in there and can see the whole filter from one angle. It is a K&N filter besides so it has less draw than a stock one in the first place.
Maybe i should just buy pods and rejet and the myth and ambiguity about the airbox will go away.. =)

Just run it and check the spark plug colors.

Earl

 

[sparkey]

Just run it and check the spark plug colors.

Earl

I will do that, but i dont need a plug chop to tell me its running lean at WOT as there is no smoke from tailpipes to tell me its running rich.....

 

[chuck hahn]

Earl.. I am not gonna argue the point..I know the 750s inside and out. Pods allow a less restricted airflow than the stock paper or foam filter..so you and others that run pods DO need to rejet. And there aren built in velocity stacks in the stock boots as well. If he has stock airbox and stock exhaust ( even though he has the Kand N ) theres just maybe a MICROSCOPIC difference. The problem he is having has nothing to do with the Kand N or the missing snorkle. I have a Kand N in my 77 750 so i know thats not the problem. First of all he stated the clips were in 3 differtent positions in the carbs. That should tell anyone that the PO and his buddies didnt have a clue and sold the bike on the cheap to this dude. Then that would automatically send a red flag on everything else in those carbs..Main jets, pilot jets,needle jets..the full monty needs inspected. If he follows what i have told him that bike will be running like a fregiht train in just a few hours tops.

 

[GS750]

http://www.jetsrus.com/a_jets_by_carburetor_type/jets_mikuni_VM11-22_main.htm

do these look like the right ones? I will probably try 120's or maybe a jet kit with multiple sizes so i have them all to try out..
I might as well buy a set of pod air cleaners for it seein it is kind of one big pod right now..

I would NOT go to 120 mains, Ive got a 1977 GS750 which is now 850'd and has Boyer CDI ignition, new coils, iridium plugs, 4-1 tranzac exhaust and K&N pods, and the original VM26ss only needed 112.5 mains.

I would say 107.5 should be the biggest you need to go for your setup with the K&N panel but make sure you seal the airbox properly

 

[sparkey]

Earl.. I am not gonna argue the point..I know the 750s inside and out. Pods allow a less restricted airflow than the stock paper or foam filter..so you and others that run pods DO need to rejet. And there aren built in velocity stacks in the stock boots as well. If he has stock airbox and stock exhaust ( even though he has the Kand N ) theres just maybe a MICROSCOPIC difference. The problem he is having has nothing to do with the Kand N or the missing snorkle. I have a Kand N in my 77 750 so i know thats not the problem. First of all he stated the clips were in 3 differtent positions in the carbs. That should tell anyone that the PO and his buddies didnt have a clue and sold the bike on the cheap to this dude. Then that would automatically send a red flag on everything else in those carbs..Main jets, pilot jets,needle jets..the full monty needs inspected. If he follows what i have told him that bike will be running like a fregiht train in just a few hours tops.

to clarify again.. these carbs were off a different bike. they were purchased from a bike yard as a unit and cleaned and adjusted by me