SuzukiSavage.com - Big Bore Bobber Build

Christof13T Full Member Offline SuzukiSavage.com Rocks! Posts: 211 Vicoria, Texas Gender:	Re: Big Bore Bobber Build Reply #225 - 03/06/18 at 08:04:21 The muffler is stock + 1 5/16" hole drilled in the back plate. The muffler is not causing a lack of vacuum at the intake...
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Re: Big Bore Bobber Build
Reply #226 - 03/06/18 at 08:18:54

Christof13T wrote on 03/06/18 at 07:58:01:

Reducing that surface area to what was available with the pancake has cured the issue of the slide failing to operate.

I am still not convinced that the issue involves your slide not moving - you really don't know where your slide is when the engine operates poorly....the problem actually could be related to an improper fuel mixture. The vacuum that allows the slide to open/close comes from the engine side of the slide - not from the intake side.

You may be far better off to put a Mikuni Round slide carb on the bike.....the CV carb is obviously not working for you.

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Christof13T Full Member Offline SuzukiSavage.com Rocks! Posts: 211 Vicoria, Texas Gender:	Re: Big Bore Bobber Build Reply #227 - 03/06/18 at 09:13:41 That is incorrect. The port on both my carbs that operates the slide is on the filter side. It is on the top side center and oval shaped and curves downward like a frown face.
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Re: Big Bore Bobber Build
Reply #228 - 03/06/18 at 09:14:04

Chris , doesn't it seem funny that racing motorcycles ,don't run air filters at all? The problem you have isn't that the slide isn't opening it's the fact that the fuel mix is going lean. what you could try rather than restricting the air intake is removing one more washer from the needle jet. your running a bigger piston the vacuum in the carb is caused by the piston moving down ,drawing fuel and air in and has little to do with the size of the air cleaner. but let's look at where the power is being made, what's happening in side the cylinder? how do you make power? air and fuel in ,BANG exhaust out! getting the exhaust out is all important! exhaust has two components ,a pressure wave and exhaust gases, the wave travels at nearly the speed of sound the gases slower. when the wave reaches the end of the header pipe some of it leaves with the gases but the rest reverses and moves back up the header as a negative pressure and if it arrives during valve overlap(rpm dependent) helps pull out the remaining exhaust gases and helps pull in more fresh fuel mix. your wave is weakened buy having a drilled muffler more of the wave is leaving with the gases, and you've restricted the incoming fuel mix . therefore you leave more exhaust gases in the cylinder and there is less room for the incoming mix (Leaner charge=less power)It seems funny to me that my stock 95 will run 88mph with only a Dyna muffler and carb jetting. your attacking the wrong end of the problem.

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Re: Big Bore Bobber Build
Reply #229 - 03/06/18 at 09:15:02

carburation is a balancing act.
The intake vacuum vs fuel level in the bowl vs atmospheric air pressure at the filter.

If you're choking the inlet to increase intake vacuum to promote the fuel ratio somethings wrong.

Do you have an air leak in the intake manifold?
Have you plugged the vacuum port?
Is your float level correct?
Are your bowl vents open?
Is your air filter clean?
Valves adjusted?
What does sparky look like?
You have 1 extra hole in the muff, what's the back pressure like?
Such as, if it were loose would it blow off when running?

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Re: Big Bore Bobber Build
Reply #230 - 03/06/18 at 09:43:27

Christof13T wrote on 03/06/18 at 09:13:41:

That is incorrect. The port on both my carbs that operates the slide is on the filter side. It is on the top side center and oval shaped and curves downward like a frown face.

The port on the top side of the intake is the vent for the bottom side of the diaphragm......the vacuum that raises the slide comes from the two holes in the bottom/front of the slide - when there is enough vacuum on the top side of the diaphragm to overcome the slide spring and the pressure at the vent on the inlet side...the slide will raise until the flow is stabilized.

By restricting the flow on the inlet side - you are actually making it harder for the engine to raise the slide.

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batman Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 3806 osceola new york Gender:	Re: Big Bore Bobber Build Reply #231 - 03/06/18 at 09:55:01 It may well be that the stock muffler is to restrictive for your larger displacement ,and has to much back pressure . You may want to do the Hartman muffler mod, it's listed in the Tech Section.
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Christof13T

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Re: Big Bore Bobber Build
Reply #232 - 03/06/18 at 15:10:58

Ok... I'm understanding a little better about which ports actually operate the slide.. and that the size of the air filter shouldn't have anything to do with slide operating...

So why does the change in available filter element surface area have such a dramatic effect on how if responds?

Batz, we have already been down the road of less washers... remember I had the whole thing backwards at one point. So even forced full rich at the needle height adjustment there was not enough fuel with a #170 main? Come on...

I just ran up to wally world and back after swapping out mirrors and pulled the windshield. I had not taken it on the highway since the last adjustment, just around here in the neighborhood. It has gobs of go. It is still running 43ish mpg while that windshield was still on it pushing 75mph for over an hour...

I'm not complaining.
If it's stupid.
And it works...

Is it stupid?

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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 17888 Camp Springs, Kentucky Gender:	Re: Big Bore Bobber Build Reply #233 - 03/06/18 at 15:51:19 Christof13T wrote on 03/06/18 at 15:10:58: So why does the change in available filter element surface area have such a dramatic effect on how if responds? You are restricting airflow - which will create more vacuum.....which will pull more fuel from the float bowl.
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Re: Big Bore Bobber Build
Reply #234 - 03/06/18 at 16:47:31

The motor is like your lung ,it has to "breath " in and out. If you have to restrict the intake to get it to run ,then maybe that's because it's not breathing out. You might try drilling more holes in the rear of the stock muffler, allowing less back pressure , keeping the holes small so that if they don't work you could refill them by using pop rivets .If it doesn't work ,your out nothing ,if it does you'll understand you need a Dyna muffler or something better. the stock muffler is bad on a stock motor ,which is why most go to the less restrictive Dyna, I can' t think that it would be better with your new piston.

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Re: Big Bore Bobber Build
Reply #235 - 03/07/18 at 09:24:40

I'd rip the filter off and see what happens.

How hard would it be to go back to stock?

How that filter attaches is important.
There are air inlets that can be covered that screws things up.

One thing is known
Change the ease of air flow in or out, and the engine is imbalanced.

Opening the intake up without opening up the exhaust and rejetting isn't gonna work.
Open the exhaust up without dealing with the intake and jetting, and you don't gain anything.
Read about
Intake Design Theory
There are some really good videos on
Exhaust header designs

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Re: Big Bore Bobber Build
Reply #236 - 03/07/18 at 10:32:51

I still thing he's restricting the intake, to match a restricted exhaust ,which balances the fuel ratio. Running 95MM 10.5: 1 piston with a stock muffler doesn't cut it. He's gone to a less restricted air cleaner . a larger hi compression piston , but done nothing to the exhaust. It's breathing in (trying),but it's not breathing out.Question, has anyone that has gone to a bigger piston using the stock muffler unmodified ?

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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 17888 Camp Springs, Kentucky Gender:	Re: Big Bore Bobber Build Reply #237 - 03/07/18 at 11:35:53 batman wrote on 03/07/18 at 10:32:51: Question, has anyone that as gone to a bigger piston using the stock muffler unmodified ? Nobody I know.....most times the muffler was one of the first things changed.
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Re: Big Bore Bobber Build
Reply #238 - 03/08/18 at 00:49:07

Dave just the point I was trying to make ,If your going to do mods you should start with a muffler that is better (less restrictive) and then tune the carb to it, and add a more open air cleaner and retune the carb again if needed ,not try to tune the carb with duct tape to try and make it work with a less than decent exhaust system.

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Re: Big Bore Bobber Build
Reply #239 - 03/08/18 at 05:48:23

Back to the beginning of all this fun...
Remember that the rebuild was due to piston/bore failure...
It was not rebuilt with the high compression piston solely chasing performance. I just wanted it to not grenade on me... the increased potential of performance was just a bonus. The bore was so bad the 1st time there was no option other than 97mm. I stuck with the high comp piston for the second build because it was insured and already paid for. Since we started with a new sleeve the 2nd build, it only got opened up to 95mm, instead of the extra 100$ or more it would have cost me to put in a 94mm. Besides the single 5/15" hole I drilled in the back plate of the muffler there were no other modifications made to hard parts.

What prompted the air filter experiment was that couple days of 28mpg...
That led us back down the rabbit hole of spacer placement on the needle... and we got that sorted out...

Then on to fueling at high rpm..
55 pilot and 155 main sorted that out...
It still ran just fine with the air filter pancake that was "designed " for this engine... interesting that the available surface area of that filter is about the same as a stock slide in cartridge for the stock airbox...

Again on to the big cone filter...
At 4 times the available surface area.
It leaned out the mix as soon as it reached the point where the slide should have opened... with it restricted to about stock airflow... it is beast mode, much more fun and stable, and getting acceptable fuel efficiency.

I'm on the lookout for a used dyna muffler set...

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