Author Topic: Dyno tuning (Read 81061 times)

scottly · « **on:** May 07, 2014, 10:34:59 pm »

Hey folks, I've made a few pulls on the dyno lately, trying to sort my carb out. All numbers are with a large-by-huge K&N filter, a free-flowing muffler, and a 60 idle jet, which has proved to be too rich. The next pull will be with a 58 idle and a 160 main.

147.5 main: 25.7 HP, 23.09 ft/lbs
152.5 main: 25.835 HP, 23.815 ft/lbs
157* main: 27.4 HP, 24.95 ft/lbs

*Drilled jets are like a box of chocolates: you never know what you get.

J6G1Z · « **Reply #1 on:** May 08, 2014, 10:19:30 am »

Looks like she wants more fuel. You are very fortunate to have a dyno available.

Do you have an exhaust sniffer or exhaust gas temperature gauge to help tune with?

Good luck & please keep posting up your jetting & tuning info.

Thanks
J.

scottly · « **Reply #2 on:** May 09, 2014, 12:34:27 am »

Yes, I do have a sniffer, but found that it didn't work well with the stock muffler, hence the swap to the Muzzy. I had the best pull yet, today, with a main drilled to "167": 28.81 HP, and 27.47 ft/lbs. More importantly, the A/F graph stayed within the readable range, instead of mostly flat-lining on the lean side (top of the bottom graph).

J6G1Z · « **Reply #3 on:** May 09, 2014, 11:53:09 am »

Here is a larger copy of the graph. It's a bit fuzzy, but still readable for the most part.

Do you think that 30HP is possible?

scottly · « **Reply #4 on:** May 09, 2014, 11:03:14 pm »

I was hoping to report 30HP tonight, but it didn't happen.

Even with the main drilled to "178", the sniffer was still leaner than optimum for max power. The next step is to modify the slide needle height, which, as I'd already looked into a while back, is a major PITA, compared to changing idle and main jets. I can drain, drop the bowl, swap both jets, reattach and prime the bowl in about 15 minutes these days.

J6G1Z · « **Reply #5 on:** May 10, 2014, 11:52:56 am »

Can you use a small washer to shim the needle up like on a regular slide operated carb?

Good luck & keep up the good work.
J.

scottly · « **Reply #6 on:** May 11, 2014, 02:15:54 am »

I rode the bike a bit today with the 178 main and a 60 idle, and I have to say it ran pretty darn well, but I still believe the stock carb is worth more HP.

I've found some .023" thick washers to use as shims for the needle. Here is a pic of the stock assembly:

scottly · « **Reply #7 on:** May 14, 2014, 12:37:18 am »

I made some dyno runs with the needle shimmed .046", and the improvement was very slight.
Does the factory manual give any theory of operation on the "air cut" valve located on the left side of the carb?

scottly · « **Reply #8 on:** May 30, 2014, 10:44:03 pm »

I played a bit with the "air cut" valve; it appears to control when the slide is allowed to rise. With no spring, the motor wouldn't idle at all, but ran OK at 3K or more. With a weaker than stock spring, it would idle, although poorly, and seemed to pull better at lower RPM than the stock spring. Not much, if any gain, can be found there, so I would not recommend messing with it.
The bike is currently jetted as follows:
idle 58
main 185
needle shimmed .046" (not sure if this is worth messing with, either.

)

J6G1Z · « **Reply #9 on:** May 31, 2014, 12:18:49 pm »

I have not had one of these carbs apart other than removing the float bowl.

Does the throttle slide have a vent hole in the bottom, next to the hole that the needle drops through? I just installed a DynoJet kit on a VT Ascot. Part of the kit is a drill bit, sized to enlarge that throttle slide vent. This (along with a lighter spring) is supposed to allow the slide to respond to throttle input faster. It's kind of a leap of faith type of thing, taking a drill to your parts & permanently changing the part. I have some more work to do on the VT Ascot, but initial impressions of the DynoJet kit are good.

Keep up the good work
J.

scottly · « **Reply #10 on:** June 01, 2014, 01:12:30 am »

I didn't notice a vent hole in the slide, and I gave it a fair amount of attention...

J6G1Z · « **Reply #11 on:** June 01, 2014, 01:04:42 pm »

You would most likely notice & remember if the slide had the small vent hole in the end. I wonder if drilling a slide vent might be something you need to enhance the throttle response.

Here is a link to the DynoJet "Tech Support" page: http://www.dynojet.com/jetkits/contact_support.aspx

You might consider giving them a phone call & seeing if they have any information that you can learn from. I had to call their Tech Dept. with a question that I had & they were very helpful.

I just don't know very much about how these CV type of carbs work.

Please keep up the good work & documentation. I'm very interested in following your progress.
J.

scottly · « **Reply #12 on:** July 15, 2014, 10:23:16 pm »

Time to update this thread! I found a PDF of the manual for the XL 500, and it has the same air cut valve, even though it doesn't have a CV type carb; once again, don't mess with it.

These last two runs were with the 58 idle and 185 main. I should add that little gain in HP was recorded after going larger than 167, but there was a slight increase in torque, and more importantly, a much better throttle response. My dealer has been very kind, allowing me to swap jets after I bought two each of idle and mains, but after a point I started just drilling the original main, as it was easier than a trip to town. I'll probably trade one of the new mains for a 190, but I'm in no rush.

J6G1Z · « **Reply #13 on:** July 16, 2014, 10:43:25 am »

Here is a bigger picture of the Dyno graph.

J.

J6G1Z · « **Reply #14 on:** July 16, 2014, 11:03:07 am »

So if I understand correctly, you have uncovered 5 horsepower with just jetting changes? That's great! Keep up the good work.

How about some pics of your bike, modifications & exhaust pipe. Have you tried the ThumperStuff header yet?

J.

scottly · « **Reply #15 on:** July 16, 2014, 11:13:46 pm »

Unfortunately, I never made a base-line run with the stock air-box and snorkel. The modification that resulted in the huge increase in main jet size the most was the K&N filter:
http://ascot500.com/index.php?topic=214.0
It would be nice to be able to post a 500K size graph; at least it would be easier to read, not to mention much easier for me to size.

J6G1Z · « **Reply #16 on:** July 17, 2014, 11:46:12 am »

I believe that a box stock FT produces about 24-26HP. So you are looking at a sizeable increase.

Do you know how much difference the muffler swap made?

Do you have a K&N in the OEM airbox, or did you remove the airbox & install the filter onto the carb inlet?

I used to run K&N filters when I lived in the Arizona desert. I found that the real fine dust would get past the filter & on into the intake tract, carb, etc. Next time you have the K&N out, take a white rag & try wiping the inside of the filtered/clean side. If the rag shows dirt, it's getting past the filter. I swapped to UNI filters & have not had the problem since.

J.

scottly · « **Reply #17 on:** July 17, 2014, 11:15:38 pm »

I can't really say how much difference the muffler made; looking back at my notes, there was no difference between the stock muffler and an open header, but the bike was still very lean at that early stage of testing.
I removed the stock airbox, and adapted the K&N filter to the stock rubber tube that attaches to the carburetor. I did apply some filter oil to the inside of the tube, and now that I've had the bike off road in dusty conditions, I should check to see if grit is making it's way past the filter.

J6G1Z · « **Reply #18 on:** July 18, 2014, 10:25:32 am »

Are you still running the original exhaust downtubes?

Have you ever had them off & looked down inside the head pipes? I was surprised by how much the inner tubing narrows down the flow path. Here are some pics & measurements that I took from the OEM head pipes & the ThumperStuff header.
http://ascot500.com/index.php?topic=138.msg1464#msg1464
I would like to see a back to back dyno testing of the header. Some folks feel that the stock FT runs better off the OEM head pipes with the smaller tubing I.D. Maybe you can wrangle a deal from Mark at ThumperStuff for testing purposes.

Good luck
J.

J6G1Z · « **Reply #19 on:** July 18, 2014, 10:37:45 am »

Quote from: scottly on July 16, 2014, 11:13:46 pm

It would be nice to be able to post a 500K size graph; at least it would be easier to read, not to mention much easier for me to size.

Some wishes can come true. At least once the Admin guy figures out the right screen to make the changes.

As far as re-sizing pictures, this program is free & I really like using it. You can do a whole batch of pics at one time. It's called: "Image Optimizer" at: http://xat.com/io/index.html

Keep up the good work
J.

scottly · « **Reply #20 on:** July 18, 2014, 07:37:08 pm »

Yes, I'm running the stock header, but I'd like to try the Thumperstuff one; unfortunately, the budget is kind of tight right now. I saw your post earlier about the ID of both pipes at the cylinder head end, so I measured the stock '82 XR pipe: 1.00".
This graph is the first one I posted, with a 167 main, overlaid with part of the second graph with the 185 main.

scottly · « **Reply #21 on:** July 18, 2014, 07:39:12 pm »

Quote from: J6G1Z on July 18, 2014, 10:37:45 am

Quote from: scottly on July 16, 2014, 11:13:46 pm
It would be nice to be able to post a 500K size graph; at least it would be easier to read, not to mention much easier for me to size.

Some wishes can come true. At least once the Admin guy figures out the right screen to make the changes.

J.

Woo Hoo!!!! That works great!!! Thanks!

AndreLindholm · « **Reply #22 on:** April 05, 2015, 10:50:27 am »

Wow thats pretty good changes. Is your engine stock other than the KN air filter and the free flowing exhaust?
Have you done anything else since?

scottly · « **Reply #23 on:** April 06, 2015, 10:57:16 pm »

Yes, the motor is stock, other than the filter and silencer. I have a used White Bros WBX-1 cam, which will probably be the next modification.

scottly · « **Reply #24 on:** May 31, 2015, 11:35:16 pm »

The bottle-neck in the stock carb appears to be the needle jet; with an ID of .101", and the needle OD about .071" at the point it enters the restriction in the jet with the slide fully open, the combination will only flow as much as a 1.824mm main jet.

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Author Topic: Dyno tuning (Read 81061 times)