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Gurgling before take off?

  • Thread starter Thread starter safwan.khan
  • Start date Start date
S

safwan.khan

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Hi guys. I have a vintage Suzuki gs450 from the late 80s. It came with NGK BP5EY spark plugs pre-installed by the previous owner who, by the way, had kept the bike in pretty nasty condition. I have overhauled the top end of the engine and adjusted valve gaps to 0.05 intake and 0.07 exhaust. It runs much smoother now however there is initial gurgling as I pull the throttle from idle position before both the cylinders finally jump in and the roaring begins. Could my spark plugs be the culprit?

I read on the internet that NGK B8ES are the ideal spark plugs for old twin cylinder bikes. But I am not sure if that really is the problem here. Please advise :)
 
By "gurgling" , do you mean hesistation, or actual sound? Do you have the stock air filter setup or something else?

I'd used the proper heat range spark plugs called for by suzuki.
 
How did you synchronize the carburetors? How did you ajust the mixture screws? You shoud use the correct spark plug for the engine, but I doubt if that's the cause of the gurgling. Most GSes take B8ES, not sure about your 450.
 
By gurgling I mean it initially hesitates before I pull the throttle a bit more and both cylinders fire up. I have a feeling as I drive her that one of the cylinders is lagging. This might be a carb adjustment issue. I balanced her carbs using the technique I saw on youtube where a guy is balancing his carbs by sticking in a pipe down the air hose of the carb and listening to the air suction sound. If it whistles evenly on both sides that means the carbs are pretty much balanced. I double checked it with my manometer however I know it is not the most accurate method out there. I do not know how else to make the balance more accurate since there are no air inlets on the carbs that match the size of my manometer tubing.

tom203 said:
By "gurgling" , do you mean hesistation, or actual sound? Do you have the stock air filter setup or something else?

I'd used the proper heat range spark plugs called for by suzuki.
Click to expand...
 
I worked with a guy who used the "listening method" when balancing european sports cars with multiple carbs- he was good at it, I was not.
If you haven't already, do a good bench sync- this ensures that both throttle plates open in same proportion at same time

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html#A01

If your carbs are clean with decent o-rings/gaskets, this will get you real close.

Did you see this link about carb cleaning?

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
 
Thanks Tom. These resources are very helpful. I'll be looking into the carb cleaning guide that you shared and after that will jump into the sync process again.:)

tom203 said:
I worked with a guy who used the "listening method" when balancing european sports cars with multiple carbs- he was good at it, I was not.
If you haven't already, do a good bench sync- this ensures that both throttle plates open in same proportion at same time

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html#A01

If your carbs are clean with decent o-rings/gaskets, this will get you real close.

Did you see this link about carb cleaning?

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
Click to expand...
 
I took my GS450 apart last night. Pulled the carbs and dismantled them thoroughly. Checked out every single detail that I could possibly look for. I found the following:

1: The float heights were 20.5 and 21mm which is low as compared to the standard 22.4mm.
2: The butterfly alignment was out. Left one was a bit more on the open side as compared to the right one.
3: One of the pilot jets was clogged.

I did the following:

1: Took off all the rubber parts from the carb including gasket and float bowl rubbers + fuel screw washers.
2: Added about 100ml vinegar to 2 litres of boiling tap water.
3: Soaked the carb body along with the jets into the boiling acid water (watching out for those butterflies)
4: After about 5 minutes of hot bath, took all the parts out and they were looking brand new.
5: Took NASA carb cleaner and blew the hell out of all the inner carb holes and gaps until I emptied the entire large can :D
6: Adjusted the float heights to be exactly at 22.4 mm on both sides and double checked whether the floats are sinking in petrol or not. Both were OK.
7: Re-assembled all the cleaned out parts after drying with an air pressure gun.
8: Adjusted the butterfly level by adjusting the alignment screw making both of them at one level.
9: I took out the filter foaming from airbox and washed that sucker with petrol and a hard tooth brush. That made my garage floor all muddy as it was completely DIRTY from the inside. Once done, put the foaming back in after cleaning with air pressure gun and then put the shining new carbs back into my GS450.
10: Checked out both her plugs. Left one was literally dripping fuel off its tip. I had Denso W24ESU plugs in her. Replaced both her plugs with NGK BP5EY as that was the only spare pair I had at home and it was working reasonably well on this bike before I took them off.
11: Filled the carbs with petrol and hit that choke before touching that self starter.
12: The engine roars up at 6000+ rpm. Adjusted the idle throttle and brought it down to 1.5 k rpm. Then adjusted the fuel screws while sticking two evenly matched pipes down the carb air hoses and balanced them out as evenly as I possibly could.

And now she runs great! :D No more lag or gurgling issues. :cool:
 
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Thanks :) well here is an update. I have noticed that she is still blackening her left spark plug and I have to periodically replace it. I have recently changed her piston rings and still into the break-in process so do not know if bad rings are causing this. I also put new valve seals on all 4 valves. Any ideas what is causing this blackness? I suspect there is engine oil in the combustion chamber and I am completely baffled. What could possibly be happening here? o.O

Note that this is happening only in the left cylinder. Right cylinder is OK.

tom203 said:
You work quickly and thoroughly!
Click to expand...
 
Last edited:
Well it was black and shiny when I pulled it out once it began misfiring. The replacement plug had already started turning black when I drove her for about 2-3 km. Also there is a little smoke coming from exhausts when I turn her engine off and let her stay parked for 30 seconds or so on a hot engine. Thick, dense, greyish white smoke.


tkent02 said:
Are the plugs black and shiny or flat black?
Click to expand...
 
Last edited:
I fixed it. When I took the cylinder head off and examined the pistons, I noticed that the ring gaps had somehow got themselves aligned with the piston pin side and therefore engine oil was being pumped into the combustion chamber on every stroke. I have replaced the rings once again and realigned them properly but still wondering what caused the piston ring gaps to rotate in such a way. Any expert opinions friends?

tkent02 said:
Black and shiny is usually an oil problem.
Click to expand...
 
But what could be its typical cause? Nothing happens without a reason. Does it have something to do with the way I do my engine break-in? This is the first time such a thing has happened to me ever since I started wrenching my rides.

tom203 said:
Random things do happen, but I think this 450 likes all the attention you've been lavishing on it!
Click to expand...
 
The problem seems to have gone away after I put a few hundred more Ks on the meter. The rings must not have seated well back at that time. :)
tom203 said:
Yes, but is the reason predictable/foreseeable ?- sometimes, no
Click to expand...
 
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