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Post by marcus081992 on Mar 25, 2018 18:50:16 GMT 1
i know you guys have been asked jetting questions a thousand times. I have a 350lc with allspeed pipes and foam filters. The bike has come with 31k carbs with standard jetting. What jet sizes would you guys recommend, for the pilot and main jet?
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Post by jessy03 on Mar 25, 2018 19:32:37 GMT 1
I’d guess 27.5 and 290
Jess
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Post by srhiskx on Mar 26, 2018 18:09:21 GMT 1
I'm in the USA but have Allspeeds on the RZ350 YPVS
Running a y boot with a big K&N filter. Stock carbs Dynajet
Kit 380 main and 30 pilot. Plug is tan and I don't have to mess with jetting for temp changes.
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Post by Tobyjugs on Mar 27, 2018 17:44:12 GMT 1
No dis-respect meant for Jessy but i would start at 400 if it is open foam filters
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Post by 4l04ever on Mar 29, 2018 18:26:30 GMT 1
Yes, foam filters = 400+ main jets :-)
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Post by 4l04ever on Mar 29, 2018 18:27:32 GMT 1
....or put a standard airbox back on and use the standard 31k jetting (240 mains).
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Post by jon on Apr 1, 2018 8:47:50 GMT 1
No dis-respect meant for Jessy but i would start at 400 if it is open foam filters Tobyjugs, I know you have experience of these foam filters and have suggested sizes based on that. I may be missing the point here somewhat but that’s a 66% increase. Now the fuel obviously has to be the same mixture (richness) as before. So does that mean with pods you get 66% more mixture into the barrels? If so that must make for a huge power increase so I suspect not otherwise everyone would be running pods. What are the real world benefits and downsides of using pod filters? Jon |
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Post by Tobyjugs on Apr 1, 2018 12:11:08 GMT 1
Don't know where to start with this question. The two stroke engine is not that efficient so i guess more fuel will also get lost in the scavenging process. I have never done this but i think if you want to see how well your engine is working, try to calculate the area under the dyno line, with foam filters or with standard air box. The simple answer is the pod filters flow air easier as they have more foam area which looks less dense than the standard foam filter I bought a second hand engine and after swapping it in and out i noticed it was a tiny bit more lively than the Bob Farnham/Higgsy engine i had. The flat spot around 6k always makes me crazy, so i went to a dyno with this engine spec; Standard Exhaust Standard carbs (250 version) Reed petals from Bob Farnham 6mm spacers fitted barrel/reed side Standard air box Ignitech Main jets 290This was set up on the dyno and i had a great bike for going from A to B although it was a little lacking in oomph. No stutter. This bike made 48 hp  The same bike and engine (no work done to engine) was now prepared for the track; TSA's normal spec Standard carbs (250 version) Reed petals from Bob Farnham 6mm spacers fitted barrel/reed side Foam filters Ignitech Main jets 460
Six 20 minute track sessions the bike used 28 litres of fuel This was set up on the dyno and it was now pushing out 60hp with the dreaded stutter, but only if you stayed in that area, WOT and you never noticed it. Not good for the LC touring club.  As for pros and cons not really sure. I would say, if you want a bike only for riding without to the hassle of too much maintenance keep it standard with the air box and regularly use it. If your like me and are constantly playing with engine parts and changing engines and exhaust pipes a pod filter is easier because it makes the removal of the carbs easier and quicker for jetting plus you are less restricted for room because there is no air box. A con is definitely less miles to the gallon because of the bigger jets. Probably frowned upon by the LC Touring Club. Also there is less support for the carbs, especially for the bigger carbs. How important is this? i have no idea. I would also like to say i find it a nightmare to roughly set the jetting. It can take a day or longer and for me its like playing cat and mouse until the plug go's brown. Every time i have ended up bigger than 400 for the main jets, except once on a standard 250 engine using 31K carbs pod filters and JL pipes. This was 390 and when the cold weather set in i went to 410 |
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Post by Tobyjugs on Apr 2, 2018 15:27:59 GMT 1
No dis-respect meant for Jessy but i would start at 400 if it is open foam filters Tobyjugs, I know you have experience of these foam filters and have suggested sizes based on that. I may be missing the point here somewhat but that’s a 66% increase. Now the fuel obviously has to be the same mixture (richness) as before. So does that mean with pods you get 66% more mixture into the barrels? If so that must make for a huge power increase so I suspect not otherwise everyone would be running pods. What are the real world benefits and downsides of using pod filters? Jon Was my answer ok for you jon |
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Post by jon on Apr 2, 2018 15:45:00 GMT 1
Thanks Tobyjugs.
What you are saying shows that it is required, but I still don’t fully understand why?
Anyway I don’t NEED to know why, so I’ll just accept it.
Jon
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Post by srhiskx on Apr 2, 2018 17:37:59 GMT 1
Tobyjugs
I see by you dyno graph you got 60 hp and still stayed
under 10k to achieve it. Do you attribute that to the pipes or the reed spacers? Just curious. Thanks Srhiskx
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Post by Tobyjugs on Apr 2, 2018 20:43:58 GMT 1
Thanks Tobyjugs. What you are saying shows that it is required, but I still don’t fully understand why? Anyway I don’t NEED to know why, so I’ll just accept it. Jon I don't fully understand the physics either more down to experience and playing about with the engines. |
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Post by Tobyjugs on Apr 2, 2018 21:09:27 GMT 1
Tobyjugs I see by you dyno graph you got 60 hp and still stayed under 10k to achieve it. Do you attribute that to the pipes or the reed spacers? Just curious. Thanks Srhiskx Hi Srhiskx i do believe the reed spacers help but i have never measured the difference on the dyno. In the last dyno-graph you are seeing the difference in the tuned length of the exhaust makes. The owner of PSTuning is a friendly man and whilst i was asking him to explain the basic theory of expansion chambers he jumped on his lathe and made two spacers to put on the expansion chambers. We added the two spacers and the effect you can see is the green line. The spacer he made was 28mm and you can see it dropped peak power down 500rpm and at 7k it is making an extra 7.5 PK. The pipes were made for another slightly bigger engine by PSTuning. I have also put TSA's on this engine and the results were very similar The TSA's were a tiny bit more peaky with 61 PK. The tuning data for this engine is documented in my other thread and shortly i will be putting it on the dyno to check the effect of modified standard reeds and reducing the the internal diameter of billet manifolds to suit standard size carbs. |
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Post by srhiskx on Apr 3, 2018 0:03:16 GMT 1
Tobyjugs I see by you dyno graph you got 60 hp and still stayed under 10k to achieve it. Do you attribute that to the pipes or the reed spacers? Just curious. Thanks Srhiskx Hi Srhiskx i do believe the reed spacers help but i have never measured the difference on the dyno. In the last dyno-graph you are seeing the difference in the tuned length of the exhaust makes. The owner of PSTuning is a friendly man and whilst i was asking him to explain the basic theory of expansion chambers he jumped on his lathe and made two spacers to put on the expansion chambers. We added the two spacers and the effect you can see is the green line. The spacer he made was 28mm and you can see it dropped peak power down 500rpm and at 7k it is making an extra 7.5 PK. The pipes were made for another slightly bigger engine by PSTuning. I have also put TSA's on this engine and the results were very similar The TSA's were a tiny bit more peaky with 61 PK. The tuning data for this engine is documented in my other thread and shortly i will be putting it on the dyno to check the effect of modified standard reeds and reducing the the internal diameter of billet manifolds to suit standard size carbs. |
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Post by srhiskx on Apr 3, 2018 0:07:37 GMT 1
Tobyjugs I see by you dyno graph you got 60 hp and still stayed under 10k to achieve it. Do you attribute that to the pipes or the reed spacers? Just curious. Thanks Srhiskx Hi Srhiskx i do believe the reed spacers help but i have never measured the difference on the dyno. In the last dyno-graph you are seeing the difference in the tuned length of the exhaust makes. The owner of PSTuning is a friendly man and whilst i was asking him to explain the basic theory of expansion chambers he jumped on his lathe and made two spacers to put on the expansion chambers. We added the two spacers and the effect you can see is the green line. The spacer he made was 28mm and you can see it dropped peak power down 500rpm and at 7k it is making an extra 7.5 PK. The pipes were made for another slightly bigger engine by PSTuning. I have also put TSA's on this engine and the results were very similar The TSA's were a tiny bit more peaky with 61 PK. The tuning data for this engine is documented in my other thread and shortly i will be putting it on the dyno to check the effect of modified standard reeds and reducing the the internal diameter of billet manifolds to suit standard size carbs. That is very interesting by adding 28mm to each pipe drop the peak down 500 rpm. How did he come up with this measurement? Can you please give me the llink to the other thread? I would like to read it and follow your dyno results for the billet manifold. Thanks srhiskx |
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Post by Tobyjugs on Apr 3, 2018 11:01:44 GMT 1
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Post by reedpete on Apr 24, 2018 12:50:35 GMT 1
Thanks Tobyjugs. What you are saying shows that it is required, but I still don’t fully understand why? Anyway I don’t NEED to know why, so I’ll just accept it. Jon Let me shed some light.... its a topic with various levels of comlexity but ill but I’ll keep it to the most important two topics which explain... Fuel is sucked through the jet due to the pressure drop in the carb Venturi compare to atmosphere. When an airbox is fitted the pressure drop is different , lower actually, because of the general flow restriction that the airbox creates. Imagine a very long pipe connected , the pressure is going to be lower going into the carb entrance than at the open end. So when you mess with the upstream and remove the airbox the jets will need to go up. next topic, why do you need to change the jet size when you tune and engine if the mixture is still needed to be the same. simple answer is that as you change porting, reeds, spacers etc the shape of the pressure pulse changes. Now unfortunately a carb isn’t a perfect linear air fuel delivery device so actually what you jet to is the average AF ratio for a particular pulse shape. So the jet has to match that average. When the shape changes most likely you need a new jet size. |
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