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Discussion Starter #1
Hi all,
I'm trying to track down a couple of answers and hoping the collective SV family has the answers. I got my wife's SV fired up yesterday (after much struggling) and was able to get it running a for a bit, but unfortunately, the carbs were pretty gummed up (bike is bone stock by the way). I pulled the carbs today and cleaned out the jets. I put everything back together and she fired up like a charm!

I welch plugs were drilled out at some point- I believe my mechanic probably drilled them out last time bike was in the shop. I live in Denver (5280 ft above sea level). Guessing he made a small adjustment to the mixture to richen it up a bit.

When I pulled the carbs and cleaned them, I made sure to gently bottom the screw out and count back the turns out, however, I'm not sure I got it right.

Here is what I'm seeing- bike fired right up with choke. After about 20 seconds, I turned the choke off and it went to idle. Over the next few minutes, I adjusted the idle screw down (I had turned it way up while chasing the starting issues) to get the idle about 1800. As I revved it up, it would slowly come down to idle. It revs up quickly, but drops down very slowly.

Would the slow response when letting go of the throttle be related to the mixture screws or the throttle cable? (or something else???). I have to pull the carbs off again as I didn't have a rebuild kit and the float bowl seals need to be replaced so can get back in there to make adjustments. Just trying to narrow down my troubleshooting before-hand.

Thanks everyone.
 

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CV carbs are very good at auto-adjusting for elevation and should not need the mixture changing. There are thousands if not millions of CV carbed bikes all around the World that may well be run at Higher elevations and I bet the owners have never even been near their carbs.

If there was an adjustment required it would be to a,"Lean" mixture as there's less oxygen higher up so the Fuel-to-Air mixture would be towards the fuel,not the air.

In your case the most common cause of lack of throttle response would be air leaks allowing too much air into the Carbs so check the Carb boots in the Air filter have not been distorted on fitment. Also spraying a bit of Carb/Brake cleaner around the carbs(not inside the air-filter) at idle can show them up if the engine speed increases.

Also if the Choke plungers are sticking there might be too much fuel getting into the engine causing it to choke a little.

Also check the Spark plugs and caps to make sure both cylinders are firing correctly. I have a cheap IR Temp gun


so can check that both my cylinders/Exhaust down-pipes are running at the same temps.

Also I use Fuel cleaner in my fuel to keep the carbs and fuel system clean and it seems to combat the Ethanol they stick in the fuel these days as well.

HTH :)
 

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Discussion Starter #3
CV carbs are very good at auto-adjusting for elevation and should not need the mixture changing. There are thousands if not millions of CV carbed bikes all around the World that may well be run at Higher elevations and I bet the owners have never even been near their carbs.

If there was an adjustment required it would be to a,"Lean" mixture as there's less oxygen higher up so the Fuel-to-Air mixture would be towards the fuel,not the air.

In your case the most common cause of lack of throttle response would be air leaks allowing too much air into the Carbs so check the Carb boots in the Air filter have not been distorted on fitment. Also spraying a bit of Carb/Brake cleaner around the carbs(not inside the air-filter) at idle can show them up if the engine speed increases.

Also if the Choke plungers are sticking there might be too much fuel getting into the engine causing it to choke a little.

Also check the Spark plugs and caps to make sure both cylinders are firing correctly. I have a cheap IR Temp gun


so can check that both my cylinders/Exhaust down-pipes are running at the same temps.

Also I use Fuel cleaner in my fuel to keep the carbs and fuel system clean and it seems to combat the Ethanol they stick in the fuel these days as well.

HTH :)
Thanks.. I’ll check all that out. When using an IR themo, where are you pointing it? Anywhere in the cylinder (as long as it’s the same place on both?) hopefully Harbor Freight‘s open.
 

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Thanks.. I’ll check all that out. When using an IR themo, where are you pointing it? Anywhere in the cylinder (as long as it’s the same place on both?) hopefully Harbor Freight‘s open.
Basically yes but if possible on the exhaust manifolds or the top bit of the down-pipes :)
 
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Discussion Starter #6
Agreed. I played with it some more and got it down to 1400 or so. Seems to idle nicely. Just got new float bowl gaskets and pilot o rings. Pulling carbs and replacing (one float bowl was leaking). Will adjust throttle play and check the pilot jets again and check temps to see how they are compared to each other. Then I’m going to try and sync them...wish me luck.
 

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Agreed. I played with it some more and got it down to 1400 or so. Seems to idle nicely. Just got new float bowl gaskets and pilot o rings. Pulling carbs and replacing (one float bowl was leaking). Will adjust throttle play and check the pilot jets again and check temps to see how they are compared to each other. Then I’m going to try and sync them...wish me luck.
This might help bit with the Balancing,


:)
 

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Discussion Starter #9
I finally got the float bowl seals, replaced everything and have the carbs/airbox back on the bike. I adjusted the throttle cables so there is sufficient play on both sides, verified that the chokes are working and the boots are all sealed so no apparent vacuum leaks. Bike fires right up and runs smoothly through the rev range once warmed. The idle is very slow to settle down. I can get it to idle at around 1400 or so, but when I rev it, the motor comes down very slowly...sometimes never back to the idle position unless I play with the idle adjustment. I think my next step is to check the pilot screws and ensure I have them balanced. I bought an IR thermometer and will be working on it again this weekend to try and dial this last bit in. Does anyone know what target temp I should be shooting for at the exhaust manifold? If I'm going to make this adjustment, I want to make sure both cylinders are not running too lean.

Thanks everyone for all the assistance.
 

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i had the same problem. when i'd rev it, it would hang at 2000 then drop to 1400. could not get the idle lower.i tried a homemade sinc tool but i think the tubes were a different length. what i ended up doing was turning the sinc screw 1/8th turn then rev it. i'd have to remove the airbox each time. i went one way and it got worse so i went the other way an 1/8th at a time eventually the rpms would drop to 1000 with no hang so i called it good.now when i'm riding about 3 to 4,000 rpms and just holding throttle i can feel a slight surge, i think the pms screws are a little off, or the sinc is not right. the bike runs very good so i'm happy.
 

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Slow to return to idle can be Carb-Balance or on refit introducing an air-leak into the Carbs usually an ill-fitting Air-filter box to Carb seal on these machines.
 

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Discussion Starter #12
Slow to return to idle can be Carb-Balance or on refit introducing an air-leak into the Carbs usually an ill-fitting Air-filter box to Carb seal on these machines.
I went through the airbox and intake connections. Boots appeared to seal well on both sides, but it's worth double checking before going down another rabbit hole.
 
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