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Discussion Starter #1
About 3 months ago I fitted a Uni filter to my carbie - many people here had suggested that this is a good way to improve performance.

Well today I finally got around to having the bike dyno'd and rejetted - it had been VERY lean after fitting the uni. (oh and I have debaffled my pipes - first stage only)

Anyway, after putting the bike on the dyno my mechanic came and had a chat - without choke the air-fuel ration was between 17 and 22 (should be around 11 to 13), with the choke on it dropped to 15 to 17. He suggested that changing the pilot jet would help rectify this problem. However, he said the biggest problem was that the uni filter was not suitable to the Vol for a couple of reasons.
Firstly, although the air-flow volume is increased, the speed of the air-flow actually decreases. This makes it more difficult for the slides on the carbie to move, thus degrading throttle response and performance.
Secondly, the air that the uni is getting is directly off the engine (ie hot). Obviously all engines work better with high density air (ie cold) so the uni is actually degrading performance.

The solution? Reject to a 32.5 pilot and re-install the OEM air box and filter (or even better a K&N filter). In my mechanics opinion this would vastly improve the overall performance my bike. I got him to rejet, and I think this has helped - in the next day or so I will put the football back on and post my results.

Sorry about the long post, but hopefully this may help some people. Will be interested on other people's thoughts/experiences.

Cougar
www.kobbers.com
 

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Mascman said:
I don't buy it.

I've had my Uni for a while now and the bike has been runing great.

At 55 mph, I can't see it sucking hot air from the motor....what would it matter if it's 90° out anyways...you can't find cool air then!?
Good points too. Very interesting read above though, gets one wondering.
 

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Discussion Starter #4
I think the main point that the mechanic was making was about the velocity of the air entering the carbie - as this is what helps the slides operate.

As to air temperature - I guarentee the temp of the air sitting around the carbie would be hotter than that entering the stock air box - heat rises!
 

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I dont have the uni nor do I plan to put one on but shouldn't you have rejetted when you went to the uni anyhow, just like with the K&N which I do have?

RR
 

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I haven't dyno'd my bike so I'm not able to give definative answers. I put on the Uni-filter at the same time that I rejetted and pulled off the pair valve. It would be hard to tell you which of the three, or perhaps all three together were responsible but I can tell you that there is no comparison in performance.

The bike was so cold blooded before that I had to ride with the choke part way out. Now I pull it out on cold mornings and push it back in within a few minutes. The bike feels about the same at highway speeds but it pulls much better in traffic.

As others have said, you needed a rejet when you put the Uni-filter on in the first place, so finding that the bike was severely lean is no surprise.

I can't dispute what the guy at the shop was tellling you, but I wonder if he wasn't trying to sell you something.

Oh, by the way, I particularly like the uncluttered look of the jugs now. That may be the biggest single benefit of the Uni-filter.
 

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Good post cougar lots of food for thought there. I'm still running all stock. If I change to any thing it will be the to put a K&N filter in the stock air box and re-jet. I like the looks of the Hyper Charger but I don't think I'll do it.
 

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Actually, if you look under there you can see that there would be QUITE an airflow coming from the front of the bike when you are cruising. Maybe an argument could be made sitting stationary it doesn't get as much air, but then it doesn't NEED it either.
 

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wiseguydave said:
Actually, if you look under there you can see that there would be QUITE an airflow coming from the front of the bike when you are cruising. Maybe an argument could be made sitting stationary it doesn't get as much air, but then it doesn't NEED it either.
Exactly, when it's sitting still, it's just idling, so performance isn't an issue...as far as cooling goes, it's water cooled, so no problem there.

Now if the bike is moving, I can guarantee that there is airflow around the filter, therefore, on my bike at least, there is no lack of performance noticed.

Somebody could put a temp probe under there and test for sure, but I personally am not too concerned. I feel that the UNI with a rejet and pipes is a great mod for the money!
 

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cougar, how many horses is/was your bike producing according to the dyno with the UNI filter and before your rejet? Then will you get another dyno test after installing the OEM filter setup? BTW ever since I switched to UNI and rejet I have not used the choke at all, even in our Indiana winters.
 

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I had an opportunity to ride a bone stock 03 Vol last friday for about 45 miles or so....in town, two lane highway, and superslab. This was the first bike I had ridden other than my own 03 Vol. My presonal Vol has been depaired, uni-filter, rejetted, V & H Cruzers, and dynoed. Being able to do a direct comparison between a stock bike and my bike it was amazing the difference in performance. I didn't buy my bike new so I had nothing to compare it too previously and accepted the performance as standard....but it is far above IMO. Can't say which performance mod made the most difference, because it was all done at the same time but I agree with others, about the choke, performance, etc. I am not a mechanic either, but do agree cold air improves performance over hot air. But when moving, the hot air is blown toward the back of the bike and the cool-er air comes from the front of the bike where the uni is located on the carb. If the air is coming from the side of the motor without a forced intake, wouldn't it delay the time for the air to get in the carb....maybe not since air is continuously flowing, just a thought though. If nothing else, I like the nekked jugs better anyway! My point was not to dispute any point, just to state my personal comparison experience.

raztus
 

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Sounds like your mechanic needs to re think what he is saying:

The slide opens by vacuum not by the airflow going down the throat of the carb. With either setup the carb is operating with negative pressure, the engine sucks the air that it needs in. The air has a straight path through the UNI vs having to go around several bends with the stock snorkle setupwhich would slow down the air velocity considerably.

I have the UNI on my bike and haven't had any problems. I've done several rejets on other bikes with different setups: K&N in stock airbox, thunder air kits and hyperchargers. I've ridden everyone that I've set up and the throttle response on mine is as good if not better than the other bikes that I have done. The throttle response of mine is definately better that the one with the Thunder Air S&S kit that I did.
 

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Thanks for the heads up. Do you know what jets were used when the uni went on? I'd bet the rejet for the Uni was not done properly. Too many people have had the Uni filter on for too long for it to be a serious problem. According to the rejet matrix it should have been....


Aftermarket or stock pipes (baffles or debaffled) & Uni filter or K&N (airbox mounted):
150 or 155 main, 37.5 pilot jet, dyno spring, dyno needle on 3rd notch, mix screw at 2.5 - 3 turns. Adjust idle knob as needed to reach 1100 rpm.
 

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Discussion Starter #17
Mascman said:
I am curious too...did you re-jet when you went to the UNI and debaffled pipes?

My bike runs great with the UNI and the V&H...better than it did with the stock debaffled pipes. It ran great with the gutted stockers too, though.
No I hadn't rejetted when the Uni went on, that was the whole purpose of getting the bike rejetted and dyno'd yesterday.

Cougar
 

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Discussion Starter #18
Mort said:
cougar, how many horses is/was your bike producing according to the dyno with the UNI filter and before your rejet? Then will you get another dyno test after installing the OEM filter setup? BTW ever since I switched to UNI and rejet I have not used the choke at all, even in our Indiana winters.
OK, with the Uni filter, but before the rejet, my Vol was putting out an earth-shattering 36 horses (at the wheel).

After the rejet to the 32.5 pilot, it now puts out 44HP. My mechanic reckons that this will improve by about another 5HP by returning to the stock ai-box. When I have the time/money I will get it re-dyno'd to confirm.

Cougar
 

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Discussion Starter #19
Wow, this post sure has started a bit of discussion.

Like many people I can only take what my mechanic says at face value. I have a limited knowledge of engines, and unlike him, I'm not a Suzuki mechanic. NO he wasn't trying to sell me anything, so I don't think he was trying to intentionally mislead me.

I have to admit that I am still a little confused - everything that people here have said about the Uni filter makes sense and sounds logical. Yet everything the mechanic said also made sense and sounded equally logical - the only problem is that they are mutually exclusive!

I guess I will go back to the stock air box and see what happens (although I did really like the look of the naked jugs).

Thanks for everyone's input and I'll keep you posted.

Cougar
 

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cougar said:
Mascman said:
I am curious too...did you re-jet when you went to the UNI and debaffled pipes?

My bike runs great with the UNI and the V&H...better than it did with the stock debaffled pipes. It ran great with the gutted stockers too, though.
No I hadn't rejetted when the Uni went on, that was the whole purpose of getting the bike rejetted and dyno'd yesterday.

Cougar
OK that explains a lot.... These bikes run lean.. Adding the Uni would make that A LOT!!! worse without a rejet.

If you don't want the football have him do this.....
150 or 155 main, 37.5 pilot jet, dyno spring, dyno needle on 3rd notch, mix screw at 2.5 - 3 turns.
Adjust idle knob as needed to reach 1100 rpm.
 
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