Banshee runs good, starts bad, low compression

[Teunie]

Hi,

I recently bought a 2009 Yamaha Banshee. Actually it's a model 2006 that has been new in a crate until 2009. I bought it from the first owner who didn't ride it much. The quad looks almost new. When I went for a test drive it was hard to start. The seller said it usually starts the first time (looked honest to me) but it has been sitting in the garage for a while and he cleaned it. The test drive was fine so I bought it.

The quad is completely stock except for Toomey T6 full pipeset and I got the remainders of a jetkit, it has 280 mainjet in it. It is still on the original pistons never been opened.
Last owner always mixes 1:30 I have improved the oil quality and went to 1:39 on the first tank.

At home it was hard to start again. Like 30 kicks. I don't have a lot of Banshee experience but it feels easy/light to kick it over. After some fiddling with the cabling, choke and reserve it started right up. It idles well, left it for 10 minutes without the choke just idling. I rode for 40 kilometers without any issues. No bottom end but it when it gets into the rpm's it pulls strong, front wheels off the ground and you can feel it pulling in your arms. There is no sputtering just accelerates really well up until about 120kmh. I also have a Raptor 700 and a V-Force 700 that should be about equally fast and it feels like that. Doesn't feel like I am missing power (only in low and mid but the Toomey seems to do that).

After I got back I checked the plugs, they were nice porcelain coffee with milk with a little bit of fresh oil around the edge of the plug.

While the bike was cooling down I changed the transmission oil. The day before I already had changed the coolant. After changing the oil I did a compression test;

Ignition off
Unplugged both sparkplugs
One plug out, connected compression test (screwed it in, finger tight), left other plug in to avoid sucking in dirt
While full throttle kicked around 15 times

The compression test went straight to 60psi but it does not get higher. Same reading in both cilinders.
Put some oil in the hole, did not do anything to the result.
Also tried with fuel on and off.

I repeated this test a few times also after starting the engine and letting it idle with some revs for around 10 minutes so the engine was warm. Always 60 or just below 60 psi.

Since I saw in this forum I should have 120 plus and often compression test sets are rubbish I connected the tester to a compressor. Let it go all the way up to 120psi and the compression tester shows the same value as the meter that is built into the compressor. So the meter should be fine as it gets above 60psi.

Next day the quad started on the first kick. I cleaned all contacts (I had some ground issues with the turn signals and also with the trailtech) there was some corrosion. I also cleaned the contacts for the ignition coil. The day after the Banshee needed 10 kicks to come to life.

Now I am cleaning the air filter and the reeds+carbs are next.

So summed up;

- Starting is sometimes hard sometimes easy
- Idles good, jetting looks right, runs well
- Compression appears to be very low. How can the quad run this well when the compression is only 60psi?

Any suggestions?
I am not eager to open it up since it runs well when I get it started but don't want to blow my engine.

[yamaha04]

What’s the elevation above sea level where you live/ride. And what the temp.  
what pilot jet does it have.   If it’s a 25. Jump up to 27.5    
secondly and I’m no expert but I don’t believe 120 psi coming off a compressor. constant pressure is the same as the pulses coming from the motor. Your compression tester has to hold each and every pulse of pressure building up till it stops.   At 60 psi I’m not even sure it would run.  But if never had a motor test that low so I don’t know for sure.    Try another tester.     Investigate the pilot jet 

[yamaha04]

Oh.  One more thing I over looked on my banshee after it sat for 4-5 maybe 6 years. When I parked it I had no intentions of letting it sit that long and I never drained the carb bowls.  They got nasty.   On one of the bowls.  I forget what one there is a choke circuit that you can’t really clean.  I had mine in an ultrasonic wash twice.   Still didn’t really clean them.     Still hard to start if it had been sitting for a week or two.      It turned out to be a clogged choke circuit down in the carb bowl.  New bowl solved this.  

Edited April 22, 2020 by yamaha04
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[ginger]

is your compression testing guage a high quality one or a cheap harbor freight?

 

The cheap ones are not accurate. but if you legit only have 60psi per cylinder, you need a top end rebuild. 

 

[Teunie]

3 hours ago, yamaha04 said:

What’s the elevation above sea level where you live/ride. And what the temp.  
what pilot jet does it have.   If it’s a 25. Jump up to 27.5    
secondly and I’m no expert but I don’t believe 120 psi coming off a compressor. constant pressure is the same as the pulses coming from the motor. Your compression tester has to hold each and every pulse of pressure building up till it stops.   At 60 psi I’m not even sure it would run.  But if never had a motor test that low so I don’t know for sure.    Try another tester.     Investigate the pilot jet 

I live in the Netherlands about 30 meters above sea level. What is strange is that it idles really well, without choke it will just keep on idling without any throttle. So I doubt the pilot yet would be wrong because then it wouldn't really idle?

[Teunie]

3 hours ago, yamaha04 said:

Oh.  One more thing I over looked on my banshee after it sat for 4-5 maybe 6 years. When I parked it I had no intentions of letting it sit that long and I never drained the carb bowls.  They got nasty.   On one of the bowls.  I forget what one there is a choke circuit that you can’t really clean.  I had mine in an ultrasonic wash twice.   Still didn’t really clean them.     Still hard to start if it had been sitting for a week or two.      It turned out to be a clogged choke circuit down in the carb bowl.  New bowl solved this.  

I will check the carbs, good one!

[Teunie]

1 hour ago, ginger said:

is your compression testing guage a high quality one or a cheap harbor freight?

 

The cheap ones are not accurate. but if you legit only have 60psi per cylinder, you need a top end rebuild. 

 

I didn't buy the cheapest but also not the most expensive. Made in China.  It's like 60 dollars. What I can do is try it on my other quad to see what compression it shows.

[ClaudeMachining]

I didn't buy the cheapest but also not the most expensive. Made in China.  It's like 60 dollars. What I can do is try it on my other quad to see what compression it shows.

Usually, cheap one doenst have the valve at the tips when you put an extention and that make the low reading.

Envoyé de mon SM-G965W en utilisant Tapatalk

[Teunie]

5 hours ago, ClaudeMachining said:

Usually, cheap one doenst have the valve at the tips when you put an extention and that make the low reading.

Envoyé de mon SM-G965W en utilisant Tapatalk
 

You mean a valve right at the point where you screw it into the hole? Mine has a presure release valve but it's near the top where the meter is.

Today I put the cleaned air filter in, and the Banshee fired right up without choke on the first kick...The air filter was black when I got it, when I cleaned it appeared to be a blue twinair filter...so it must have been pretty clogged...

[Teunie]

Hmm today I started it with one or two kicks, let it idle for 10min. Shut off to add fuel, then it wouldn't start. Had to kick if forever and suddenly it started. Did not run well. Like when you have a nose-cold. The higher rpm's it started pulling like a maniac but sputtering at low and mid without any power.

Beginning to wonder if I have to take it apart.

Last thing to check before this is carbs and reeds. Will try that this weekend.

[the boris]

If you have cheep compression test they often don't have check valve at the very bottom, where it screws into the cylinder and don't read right.

Sent from my VOG-L29 using Tapatalk

[Teunie]

Hi, well, it has been some time but I don't have a lot of spare time because of my job.

Anyways I ordered a hose with a check valve at the bottom for my compression tester and now it reads between 80 and 90 psi on a hot engine. So coming from 60 that is a lot better. Seeing these results, might as well be 100 psi because of inaccurate reading so it's not convincing for me to tear up the engine...Or what would you do?

In the meantime I cleaned the carbs, after that one was leaking fuel out of the overflow I had to change the float hight to make it stop. Also I replaced the reeds that in fact still looked brand new.

The Banshee feels allright through the gears but flat out in 6th gear when I open the throttle wide open to get to top speed.
Also it will some times pop out of gear and right back in, that sounds like a clutch issue.

I also received an after market filter with adapter, when I ordered it I thought it was K&N but now I see it is somewhat misleading and the filter is not actual K&N. Here in the Netherlands the billet adapter to mount a K&N is almost impossible to get so I think it was still a good deal although I am disappointed that it is not in fact a K&N filter.

https://www.ebay.com/itm/Yamaha-YFZ350-Banshee-K-N-Style-Air-Filter-Reusable-After-Market-Stock-Airbox/264580220561?hash=item3d9a35c691:g:NegAAOSw2aJefOPu

With the new adapter and filter mounted to the stock airbox I cannot get the lid on anymore. I test drove yesterday and it pulls very well through the gears (also I notice more power in the lower RPM) but in 6th gear it won't do much after 3/4 throttle. With 3/4th throttle it actually increased speed more than with wide open. So I suspect I might still be running rich even with the open airbox. When I pull out the choke to the first notch, with wide open throttle, it bogs down pretty bad I have to release the choke or the engine will die. Should I drop a size on the mainjet?

Edited July 14, 2020 by Teunie

[Teunie]

Ah and one more question, I bought a set of new wheels and tires for street use (Goldspeed Dirt Devil with 18 inch rears) and upgraded the front sprocket to 15 tooth. However, I am still getting a low top speed of around 110 km/h. Will the Banshee fit a 16 tooth front sprocket? Because now with the 15 tooth it already looks kind of tight with the chain close to the casing.

[Teunie]

Well seems I am a real n00b and forgot the basics. Yesterday it wouldn't start so I checked and no spark. So the starting issue is an electrical problem. My Banshee doesn't have a kill switch so I unplugged the on/off key and bypassed that. At first still didn't work but after a few kicks it started. After that I used a multimeter to check if the on/off key works and it does, every time. I cleaned the connectors and reconnected the key and it still started right up. Strange, maybe just lucky. So I went over the bike and disconnected/cleaned/reconnected most of the connectors including the TORS and CDI connectors. Also the grounding for the CDI was really dirty and could use a good cleaning. Hope the issue is solved now.

I did a test run and still with the open filter box and still same results, running strong to 3/4 throttle and then not much there. I put the lid back on (doesn't really fit anymore due to the new filter mount, so the front of the lid is actually open and the back is closed) and apparently this provides a good airflow because the difference is night and day, the Banshee runs a lot better really pulling my arms when I open the throttle.

So I guess I can remove the airbox lid and then go up from 280 to 290 mainjet maybe?

Edited July 20, 2020 by Teunie